Mistaking your own body part as a separate being

You see this situation a lot in comedic cartoons like Tom & Jerry: character sees/feels what they believe is the body part (e.g. tail) of another character and proceeds to attack, trap, or otherwise do some other negative action on it, only to realize too late that its their own body part that they've misidentified.

Other times, the character "knowingly" chases/attacks their own body part, usually to show that they're dumb/crazy/weird.

In fact, this is Truth in Television: just look at how often cats and dogs chase, grab and bite their own tails.

Do we have a trope for this?