Insidious doesn't even begin to describe them.

Squirrels Heat Own Tails to Fend Off Rattlesnakes

To protect their young against rattlesnakes, California ground squirrels have evolved a special defense — they heat their tails.
Squirrels in the wild wave their bushy tails at snakes in order to look bigger and more threatening.

Infrared image of a California ground squirrel during an encounter with a rattlesnake.

After reading about the espionage squirrels let loose in Iran, is this any surprise? I wouldn't doubt if there's some super-secret organization out there right now equipping squirrels for the eventual takeover of all mankind. These types of defenses must be the result of years of work by some mastermind, sort of like Q in the James Bond movies.

(or, it could simply be the creative genius of God at work in equipping an animal with an unbelievably complex structure for it's defense)