cats

Yup. Best solution I've heard of for stuff like this out climbing in the drier is to scare the ever living daylight out of them (without doing any actual harm).

In this scenario, I would "trap" their arm with something like a notebook, make a loud racket in the fridge, and maybe even shake the door a bunch.

For something like a clothes drier, I would slap the machine a lot and shake it all about.

Basically, scare them enough that they lose all desire to do it again. Sucks to have to do it, but it's not like you can sit them down and have a chat about the dangers of machines....