It causes injuries and loss of circulation. Snares are wire strangulation noose that tightens around an animal's neck or body. It is usually used on fences to hang animals or under water to drown animals. This is a picture of a poor fox caught in a trap that is used for catching animals. The animals are stuck in the trap for hours or even days before the trapper comes to pick them up.
Some animals try to chew and bite their own limbs off just to get out of the trap.
That sure speaks volumes about the pain they must be in. When the animal finally is killed, it's not quick and painless. The trapper's main priority is the fur, so the objective is to kill the animal without damaging the fur, which can lead to especially cruel methods. Here's a trapper standing on a coyote's neck in order to suffocate the poor animal. Fur also comes from 'fur farms'.