the fish looses its body balance
To make the fish swim.
yes, their dorsal and pectoral fins have a sharp spine that can cut you
they die
Wasp fish are poisonous and spiny. If you touch their fins or spine, you can get badly cut and poisoned. In addition, wasp fish have been known to eat smaller fish.
yES THEY DO CUT THE FINS IN THE KILLER WHALES IN THE TUNDRA
They cut it with a knife
A fish can get a cut in many ways, from a toy castle or object put into the fishbowl or wherever you are keeping the fish. It may also come from the small rocks you can find in where you are keeping your fish. If it is not a pet fish, a 'wild fish' it may have gotten into a tussle with another fish, or something in the ocean or lake may have cut it. If your pet fish has a cut, i would recommend taking it to a vet, before anything worse happens from it.
blade
Stop killing them and cut their fins down
Sounds like a blood parrot, one of the most unfortunate fish in the hobby. The 'normal' blood parrot is a hybrid cichlid and is quite aggressive. Its awkward shape means it already has, in my opinion, quality-of-life issues. As if this was not enough, some people have decided that it's highly amusing to tattoo, dye, or cut fins off these fish. The taillessness is not natural - the fish has been deliberately mutilated, somebody has intentionally cut off its tail. This is generally done with a pair of scissors and no anaesthetic. If you do not already own this fish I strongly recommend you do not buy it; the less people support the cruel trade in 'cosmetically enhanced' fish, the better.
If you mean "Can a fish heal a cut?", the answer is yes.
Balsa fins refer to the fins that are made for model rocketry and are cut from balsa wood. These are glued or cemented onto the base of the cylindrical part of the rocket. They are crucial to the flight stability of the rocket.