Electrical current can only kill an animal if the current flows through the animal (it’s brain or heart) to ground. So if the squirrel is on a hot wire, it cannot get killed. Now if the squirrel gets rained on and gets wet, and comes in contact, say, with it’s nose on the hot wire and it’s tail touching the ground wire, the squirrel may get killed. But the current may only flow through the animal’s fur and not kill it. I saw such a squirrel and it’s head was messed up bad, infected and all black, and it’s tail was burnt ½ way off and the burnt part was split in two. The squirrel survived, the dead parts of it’s tail fell off and it had a very noticeable hole in one ear.
But some animals will eat stuff that will kill them, such as poisoned meat. Cows and horses may eat loco weed, etc. A dog may chew up and swallow a rag that will plug it’s guts and kill it.
Animals, like bees, wasps, spiders, may bite when being sat on or squished, as a self defense act.
No body is perfect, and neither are animals.