Nick your chin while you shave. Or catch your thumb on the sharp lid of a can. It bleeds for a bit... and then it stops.

You didn't do a thing. A crew of tiny cells did it for you. They raced to the cut, grabbed the torn edge, and called in more help. In a few minutes they had built a plug.

Here's the thing. That same sticky crew rides in every drop of your blood right now. You want it fast at a cut. But you don't want it jumpy where there's no cut at all. A clump in the wrong place can block a vessel.

So which way does your crew lean? Most of us never ask. And a cheap, fuzzy fruit may tip the answer a little in your favor...

Let me explain...

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In 1882, a young doctor in Turin, Italy, tried something bold. His name was Giulio Bizzozero. Instead of a dry smear of blood on a glass slide, he watched live blood flow through the thin vessels of rabbits and guinea pigs that had been put to sleep.

A German scientist had seen small specks in blood years before. He thought little of them. Bizzozero kept his eye on what the specks did. When a vessel wall was hurt, they piled up at that spot. They stuck to the wound, then to each other. A plug grew right where the wall was torn.

He gave them a name: piastrine. It means "little plates." In English we call them platelets.

Not everyone believed him at first. Of course, he was right. Today, the standard blood count at a checkup tallies them.

Your bone marrow turns out new platelets all day, every day. Each one lives only about eight to ten days. Your lab report counts them in a speck of blood about the size of a pinhead. A normal count runs from about 150,000 to 450,000 in that speck.

Here's how the plug gets built. A platelet floats along until it hits a tear. Under the smooth lining of every vessel sits a tough fiber called collagen. When that fiber is bared, the platelet grabs it. Then it lets out a chemical alarm. That call tells more platelets to pile on.

The alarm is what makes the crew so fast. But it's also the risk. In some people, the crew answers harder than it needs to.

Doctors can test this in a tube. They add the alarm chemical, or the bare fiber, to a blood sample. Then they time how fast the platelets clump. Take a look at what one lab found when it tried fruit...

The dish test: At the Rowett Research Institute in Aberdeen, Scotland, a team dripped water extracts of common fruits into human blood. Tomato and kiwi each blocked roughly three-quarters of the clumping. Apple and pear blocked almost none.

The scientist who led that work was Asim Duttaroy. He knew a dish is not a body. So he took the kiwi with him to the University of Oslo in Norway, and tested it in people.

His first trial was small. Healthy adults ate two or three kiwis a day for 28 days. Their blood was checked before and after, and compared with a stretch without the fruit. Clumping fell by 18%. Two kiwis worked about as well as three.

Then came a bigger test. An Oslo team signed up 102 men, aged 44 to 74. All of them smoked. For eight weeks, one group added three kiwis a day. Men in a second group got a whole basket of other foods rich in plant compounds. A third group changed nothing.

In the kiwi group, clumping fell 15%. The basket group didn't see that change.

That part matters. It hints that something in the kiwi itself does the work, not just "eat more fruit."

So what is it? Nobody can name it yet. Duttaroy's lab found the active part is small, mixes into water, and holds up even when boiled. In the dish, it worked mostly on the alarm chemical and the bare fiber. It did much less on the route aspirin blocks. You see, it seems to act in its own way. That doesn't make it a stand-in for any pill.

Short trials only tell you so much. So it helps to look at how people eat on their own.

In Spain, a network of family-doctor clinics, run out of the La Alamedilla Health Centre in Salamanca, checked 1,469 adults. People who ate at least one kiwi a week had less fibrinogen in their blood. That's the protein that spins the threads holding a clot together. Their odds of a high reading were about a third lower.

The team adjusted for age, weight, exercise, alcohol, and how much other fruit people ate. Even so, the link held.

Now, here's where I slow down. A tube test of clumping is not the same as fewer clots in real life. I couldn't find a single study that followed kiwi eaters to see if they had fewer clots. Both Oslo trials were small and short. Duttaroy also filed a patent on a kiwi extract through his university, so he had a stake in the idea. And the Spanish study was one snapshot in time.

Still, three kinds of tests point the same way. A dish. Two trials. A crowd of real eaters. For a fruit that costs less than a cup of coffee, I'd call that worth a try.

In the first Oslo trial, a third kiwi added little over the second. Eat them whole. Cut one in half and scoop it with a spoon, or rinse it and bite in, fuzz and all. The trials used plain fruit, never juice or pills.

In the Aberdeen dish, tomato matched kiwi almost step for step. The tomato's active part also survived boiling. So on days the kiwis run out, a sliced tomato or a bowl of tomato soup keeps the habit going.

If you take aspirin, warfarin, or any pill that slows clotting, talk to your doctor before you add kiwis every day. The effects could stack. Kiwi also carries some vitamin K, so with warfarin, keep your amount steady. Have surgery coming up? Tell your surgeon.

Bizzozero needed a microscope and a sleeping guinea pig to see his little plates at work. You'll never see yours. But they show up every time you nick yourself, and they're riding along right now.

You can help them keep their cool. Pick up a bag of kiwis today. Eat two tomorrow morning. Then keep going for four weeks.