How do pregnancy tests work? - Tien Nguyen

9,442,340 views ใƒป 2015-07-07

TED-Ed


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: Tal Dekkers
00:06
The earliest known pregnancy test dates back to 1350 BC in Ancient Egypt.
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ื‘ื“ื™ืงื•ืช ื”ื”ืจื™ื•ืŸ ื”ื™ื“ื•ืขื•ืช ื”ืจืืฉื•ื ื•ืช ืžืชื•ืืจื›ื•ืช ืœ 1350 ืœืคื ื™ ื”ืกืคื™ืจื” ื‘ืžืฆืจื™ื™ื ื”ืขืชื™ืงื”.
00:12
According to the Egyptians,
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ืœืคื™ ื”ืžืฆืจื™ื,
00:14
all you have to do is urinate on wheat and barley seeds, and wait.
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ื›ืœ ืžื” ืฉืฆืจื™ืš ืœืขืฉื•ืช ื”ื•ื ืœื”ืฉืชื™ืŸ ืขืœ ื–ืจืขื™ ื—ื™ื˜ื” ื•ืฉืขื•ืจื”, ื•ืœื—ื›ื•ืช.
00:20
If either sprouts, congratulations, you're pregnant!
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ืื ื”ื ื ื•ื‘ื˜ื™ื, ืžื–ืœ ื˜ื•ื‘, ืืช ื‘ื”ืจื™ื•ืŸ!
00:23
And if wheat sprouts faster, it's a girl, but if barley, it's a boy.
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ื•ืื ื”ื—ื™ื˜ื” ื ื•ื‘ื˜ืช ืžื”ืจ ื™ื•ืชืจ, ื–ื• ื‘ืช, ืื ื”ืฉืขื•ืจื”, ื–ื” ื‘ืŸ.
00:28
In 1963, a small study reproduced this test
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ื‘ 1963, ืžื—ืงืจ ืงื˜ืŸ ืฉื—ื–ืจ ืืช ื”ืชื•ืฆืื•ืช
00:32
and found that it predicted pregnancy with a respectable 70% accuracy,
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ื•ืžืฆื ืฉื”ื•ื ืฆืคื” ื”ืจื™ื•ื ื•ืช ื‘ื”ืฆืœื—ื” ืฉืœ 70%,
00:37
though it couldn't reliably tell the sex of the baby.
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ืœืžืจื•ืช ืฉื”ื•ื ืœื ื™ื›ืœ ืœื–ื”ื•ืช ื‘ืฆื•ืจื” ืืžื™ื ื” ืืช ืžื™ืŸ ื”ืชื™ื ื•ืง.
00:40
Scientists hypothesized that the test worked
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ืžื“ืขื ื™ื ืžืฉืขืจื™ื ืฉื”ื‘ื“ื™ืงื” ืขื‘ื“ื”
00:43
because pregnant women's urine contains more estrogen,
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ืžืคื  ืฉืฉืชืŸ ืฉืœ ื ืฉื™ื ื‘ื”ืจื™ื•ืŸ ืžื›ื™ืœ ื™ื•ืชืจ ืืกื˜ืจื•ื’ืŸ,
00:46
which can promote seed growth.
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ืฉื™ื›ื•ืœ ืœืงื“ื ื’ื“ื™ืœืช ื–ืจืขื™ื.
00:48
Now it's easy to take this ancient method for granted
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ืขื›ืฉื™ื• ื–ื” ืงืœ ืœืงื—ืช ืืช ื”ืฉื™ื˜ื” ื”ื™ืฉื ื” ื”ื–ื• ื›ืžื•ื‘ื ืช ืžืืœื™ื”
00:52
because modern pregnancy tests give highly accurate results within minutes.
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ืžืคื ื™ ืฉื‘ื“ื™ืงื•ืช ื”ืจื™ื•ืŸ ืžื•ื“ืจื ื™ื•ืช ื ื•ืชื ื•ืช ืชื•ืฆืื•ืช ืžืื•ื“ ืžื“ื•ื™ื™ืงื•ืช ืชื•ืš ื“ืงื•ืช.
00:57
So how do they work?
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ืื– ืื™ืš ื”ืŸ ืขื•ื‘ื“ื•ืช?
00:59
Over-the-counter pregnancy tests are all designed to detect one thing:
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ื‘ื“ื™ืงื•ืช ื”ืจื™ื•ืŸ ื‘ื™ืชื™ื•ืช ืžืชื•ื›ื ื ื•ืช ืœื–ื”ื•ืช ื“ื‘ืจ ืื—ื“:
01:03
a hormone called HCG.
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ื”ื•ืจืžื•ืŸ ืฉื ืงืจื HCG.
01:05
HCG is produced in the earliest stages of pregnancy
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HCG ืžื™ื™ื•ืฆืจ ื‘ืฉืœื‘ื™ื ื”ืจืืฉื•ื ื™ื ื‘ื™ื•ืชืจ ืฉืœ ื”ื”ืจื™ื•ืŸ
01:09
and starts a game of telephone
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ื•ืžืชื—ื™ืœ ืžืฉื—ืง ืฉืœ ื˜ืœืคื•ืŸ
01:10
that tells the body not to shed the inner lining of the uterus that month.
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ืฉืื•ืžืจ ืœื’ื•ืฃ ืœื ืœื”ืฉื™ืœ ืืช ื”ืฆื™ืคื•ื™ ื”ืคื ื™ืžื™ ืฉืœ ื”ืจื—ื ื‘ืื•ืชื• ื—ื•ื“ืฉ.
01:15
As the pregnancy progresses,
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ื›ืฉื”ื”ืจื™ื•ืŸ ืžืชืงื“ื,
01:16
HCG supports the formation of the placenta,
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HCG ืชื•ืžืš ื‘ื™ืฆื•ืจ ืฉืœ ื”ืฉืœื™ื”,
01:19
which transfers nutrients from mother to fetus.
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ืฉืžืขื‘ื™ืจื” ื—ื•ืžืจื™ื ืžื–ื™ื ื™ื ืžื”ืื ืœืขื•ื‘ืจ.
01:23
The test starts when urine is applied to the exposed end of the strip.
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ื”ื‘ื“ื™ืงื” ืžืชื—ื™ืœื” ื›ืฉืฉืชืŸ ืžื’ื™ืข ืœืงืฆื” ื”ื—ืฉื•ืฃ ืฉืœ ื”ืจืฆื•ืขื”.
01:28
As the fluid travels up the absorbent fibers,
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ื›ืฉื”ื ื•ื–ืœ ื ืข ื‘ืžืขืœื” ื”ืกื™ื‘ื™ื ื”ืกื•ืคื’ื™ื,
01:30
it will cross three separate zones, each with an important task.
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ื”ื•ื ื™ื—ืฆื” ืฉืœื•ืฉื” ืื–ื•ืจื™ื ื ืคืจื“ื™ื, ื›ืœ ืื—ื“ ืขื ืžืฉื™ืžื” ื—ืฉื•ื‘ื”.
01:35
When the wave hits the first zone, the reaction zone,
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ื›ืฉื”ื’ืœ ืคื•ื’ืข ื‘ืื–ื•ืจ ื”ืจืืฉื•ืŸ, ืื–ื•ืจ ื”ืชื’ื•ื‘ื”,
01:38
Y-shaped proteins called antibodies will grab onto any HCG.
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ื—ืœื‘ื•ื ื™ื ื‘ืฆื•ืจืช Y ืฉื ืงืจืื™ื ื ื•ื’ื“ื ื™ื ื™ืชืคืกื• ื›ืœ HCG.
01:44
Attached to these antibodies is a handy enzyme
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ืื ื–ื™ืžื™ื ืžื•ืขืœื™ื ืžื—ื•ื‘ืจื™ื ืœื ื•ื’ื“ื ื™ื
01:47
with the ability to turn on dye molecules, which will be crucial later down the road.
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ืขื ื”ื™ื›ื•ืœืช ืœื”ื“ืœื™ืง ืžื•ืœืงื•ืœื•ืช ืฆื‘ืข, ืฉื™ื”ื™ื• ื—ื™ื•ื ื™ื•ืช ื‘ื”ืžืฉืš ื”ื“ืจืš.
01:53
Then the urine picks up all the AB1 enzymes
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ืื– ื”ืฉืชืŸ ืื•ืกืฃ ืืช ืื ื–ื™ื AB1
01:56
and carries them to the test zone, which is where the results show up.
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ื•ื ื•ืฉื ืื•ืชื ืœืื–ื•ืจ ื”ื‘ื“ื™ืงื”, ืฉื ื”ืชื•ืฆืื•ืช ื ืจืื•ืช.
02:00
Secured to this zone are more Y-shaped antibodies
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ืžืื•ื‘ื˜ื—ื™ื ืœืื–ื•ืจ ื”ื–ื” ื™ืฉ ืขื•ื“ ื ื•ื’ื“ื ื™ื ื‘ืฆื•ืจืช Y
02:03
that will also stick to HCG on one of its five binding sites.
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ืฉื’ื ื™ืชื—ื‘ืจื• ืœ HCG ื‘ืื—ื“ ืžื—ืžืฉืช ืื–ื•ืจื™ ื”ื—ื™ื‘ื•ืจ ืฉืœื™.
02:08
Scientists call this type of test a sandwich assay.
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ืžื“ืขื ื™ื ืงื•ืจืื™ื ืœืกื•ื’ ื”ื–ื” ืฉืœ ื‘ื“ื™ืงื” ื—ื™ื‘ื•ืจ ืกื ื“ื•ื•ืฅ'.
02:12
If HCG is present, it gets sandwiched between the AB1 enzyme and AB2,
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ืขื HCG ื ื•ื›ื—, ื”ื•ื ื ื›ื ืก ื‘ื™ืŸ ื”ืื ื–ื™ืžื™ื AB1 ื• AB2,
02:19
and sticks to the test zone,
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ื•ื ื“ื‘ืง ืœืื–ื•ืจ ื”ื‘ื“ื™ืงื”,
02:20
allowing the attached dye-activating enzyme to do its job
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ื•ื›ืš ืžืืคืฉืจ ืœืื ื–ื™ื ืžืคืขื™ืœ ื”ื“ื™ื• ืœืขืฉื•ืช ืืช ืขื‘ื•ื“ืชื•
02:24
and create a visible pattern.
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ื•ืœื™ืฆื•ืจ ืชื‘ื ื™ืช ื ืจืื™ืช.
02:26
If there's no HCG, the wave of urine and enzymes just passes on by.
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ืื ืื™ืŸ HCG, ื”ื’ืœ ืฉืœ ื”ืฉืชืŸ ื•ื”ืื ื–ื™ืžื™ื ืคืฉื•ื˜ ืขื•ื‘ืจื™ื.
02:31
Finally, there's one last stop to make, the control zone.
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ืœื‘ืกื•ืฃ, ื™ืฉ ืขืฆื™ืจื” ืื—ืช ื ื•ืกืคืช, ืื–ื•ืจ ื”ื‘ื™ืงื•ืจืช.
02:36
As in any good experiment,
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ื›ืžื• ื‘ื›ืœ ื ื™ืกื•ื™ ื˜ื•ื‘,
02:38
this step confirms that the test is working properly.
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ื”ืฉืœื‘ ื”ื–ื” ืžืืฉืจ ืฉื”ื‘ื“ื™ืงื” ืขื•ื‘ื“ืช ื ื›ื•ืŸ.
02:41
Whether the AB1 enzymes never saw HCG,
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ื‘ื™ืŸ ืื ืื ื–ื™ื AB1 ืจืื” ืื™ ืคืขื HCG,
02:44
or they're extras because Zone 1 is overstocked with them,
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ืื• ืฉื”ื ืขื•ื“ืคื™ื ืžืคื ื™ ืฉืื–ื•ืจ 1 ืžืœื ื‘ื”ื,
02:48
all the unbound AB1 enzymes picked up in Zone 1 should end up here
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ื›ืœ ื” AB1 ื”ืœื ืงืฉื•ืจื™ื ืฉื ืืกืคื• ื‘ืื–ื•ืจ 1 ื™ื’ื™ืขื• ืœืคื”
02:53
and activate more dye.
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ื•ื™ืคืขื™ืœื• ืขื•ื“ ื“ื™ื•.
02:55
So if no pattern appears, that indicates that the test was faulty.
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ืื– ืื ืืฃ ื“ื•ื’ืžื” ืœื ืžื•ืคื™ืขื”, ื–ื” ืžืจืื” ืฉื”ื‘ื“ื™ืงื” ื”ื™ืชื” ืชืงื•ืœื”.
03:00
These tests are pretty reliable, but they're not failproof.
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ื”ื‘ื“ื™ืงื•ืช ื”ืืœื• ื”ืŸ ื“ื™ ืืžื™ื ื•ืช, ืื‘ืœ ื”ื ืœื ืžื•ืฉืœืžื•ืช.
03:03
For instance, false negatives can occur
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ืœื“ื•ื’ืžื”, ืชื•ืฆืื•ืช ืฉืœื™ืœื™ื•ืช ืœื ื ื›ื•ื ื•ืช ื™ื›ื•ืœืช ืœื”ืชืจื—ืฉ
03:05
if concentrations of HCG aren't high enough for detection.
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ื”ื ื”ืจื™ื›ื•ื–ื™ื ืฉืœ HCG ืœื ื’ื‘ื•ื”ื™ื ืžืกืคื™ืง ืœื’ื™ืœื•ื™.
03:09
After implantation, HCG levels double every two to three days,
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ืื—ืจื™ ื”ื”ืชื—ื‘ืจื•ืช, ืจืžื•ืช ื” HCG ืžื•ื›ืคืœื•ืช ื›ืœ ื™ื•ืžื™ื™ื ืฉืœื•ืฉื”,
03:13
so it may just be too early to tell.
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ื›ืš ืฉื–ื” ืคืฉื•ื˜ ื™ื›ื•ืœ ืœื”ื™ื•ืช ืžืงื“ื ืžื“ื™ ืœื“ืขืช.
03:16
And beverages can dilute the urine sample,
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ื•ืžืฉืงืื•ืช ื™ื›ื•ืœื™ื ืœื“ืœืœ ืืช ื”ืฉืชืŸ,
03:18
which is why doctors recommend taking the test first thing in the morning.
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ืœื›ืŸ ืจื•ืคืื™ื ืžืžืœื™ืฆื™ื ืœืขืฉื•ืช ืืช ื”ื‘ื“ื™ืงื” ื“ื‘ืจ ืจืืฉื•ืŸ ื‘ื‘ื•ืงืจ.
03:22
On the other hand, false positives can come from other sources of HCG,
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ืžืฆื“ ืฉื ื™, ืชื’ื•ื‘ื•ืช ื—ื™ื•ื‘ื™ื•ืช ืœื ื ื›ื•ื ื•ืช ื™ื›ื•ืœืช ืœื”ืชืจื—ืฉ ืžืžืงื•ืจื•ืช ืื—ืจื™ื ืฉืœ HCG.
03:27
like IVF injections, ectopic pregnancies,
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ื›ืžื• ื–ืจื™ืงื•ืช IVF, ื”ืจื™ื•ื ื•ืช ืืงื˜ื•ืคื™ื™ื,
03:30
or certain cancers such as uterine cancer or testicular cancer,
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ืื• ืกื•ื™ื’ื™ื ืžืกื•ื™ื™ืžื™ื ืฉืœ ืกืจื˜ืŸ ืจื—ื ืื• ืกืจื˜ืŸ ืืฉื›ื™ื,
03:34
making it possible for one of these tests to tell a man he's pregnant.
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ืžื” ืฉื™ื›ื•ืœ ืœื’ืจื•ื ืœื’ื‘ืจ ืœืงื‘ืœ ืชื•ืฆืื” ืฉื”ื•ื ื‘ื”ืจื™ื•ืŸ.
03:39
The best way for a woman to find out for sure is at the doctor's office.
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ื”ื“ืจืš ื”ื›ื™ ื˜ื•ื‘ื” ืœืื™ืฉื” ืœื“ืขืช ื‘ื‘ื˜ื—ื•ืŸ ื”ื™ื ืืฆืœ ื”ืจื•ืคื.
03:43
The doctors are also looking for HCG,
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ื”ืจื•ืคื ื’ื ืžื‘ื™ื˜ ื‘ HCG,
03:46
but with tests that are more sensitive and quantitative,
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ืื‘ืœ ืขื ื‘ื“ื™ืงื•ืช ื™ื•ืชืจ ืจื’ื™ืฉื•ืช ื•ืžื™ื“ืชื™ื•ืช,
03:49
which means they can determine the exact level of HCG in your blood.
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ืžื” ืฉืื•ืžืจ ืฉื”ื ื™ื›ื•ืœื™ื ืœืงื‘ื•ืข ืืช ื”ืจืžื” ื”ืžื“ื•ื™ื™ืงืช ืฉืœ HCG ื‘ื“ื.
03:54
A few minutes can feel like forever
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ื›ืžื” ื“ืงื•ืช ื™ื›ื•ืœื•ืช ืœื”ืจื’ื™ืฉ ื›ืžื• ื ืฆื—
03:56
when you're waiting on the results of a pregnancy test.
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ื›ืฉืืชื ืžื—ื›ื™ื ืœืชื•ืฆืื” ืฉืœ ื‘ื“ื™ืงื” ื”ืจื™ื•ืŸ.
04:00
But in that brief time, you're witnessing the power of the scientific method.
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ืื‘ืœ ื‘ื–ืžืŸ ื”ืงืฆืจ ื”ื–ื”, ืืชื ืขื“ื™ื ืœื›ื•ื— ืฉืœ ื”ืฉื™ื˜ื” ื”ืžื“ืขื™ืช.
04:04
That one little stick lets you ask a question,
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ื”ืžืงืœ ื”ืงื˜ืŸ ื”ื–ื” ืžืืคืฉืจ ืœื›ื ืœืฉืื•ืœ ืฉืืœื”,
04:07
perform a controlled experiment,
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ืœื‘ืฆืข ื ื™ืกื•ื™ ืžื‘ื•ืงืจ,
04:09
and then analyze the results to check your original hypothesis.
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ื•ืื– ืœื ืชื— ืืช ื”ืชื•ืฆืื•ืช ื›ื“ื™ ืœื‘ื“ื•ืง ืืช ื”ื”ืฉืขืจื” ื”ืจืืฉื•ื ื™ืช ืฉืœื›ื.
04:13
And the best part is you won't even have to wait until the next harvest.
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ื•ื”ื—ืœืง ื”ื˜ื•ื‘ ื‘ื™ื•ืชืจ ื”ื•ื ืฉืืชื ืœื ืชืฆื˜ืจื›ื• ืืคื™ืœื• ืœื—ื›ื•ืช ืœืงืฆื™ืจ ื”ื‘ื.
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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