Casper looks like your typical ghost but cuter, which makes it hard for him to fully cross the afterlife, because there is a stupid requirement that they should at least scare 10 people before passing through.

He? Well he scared 10 people already with a negative sign before the number.

You caught him picking some flowers in your garden and he smiled and waved in reflex, when he should be scaring you. Once it hit him, he placed his arms above his head and said "Boo...?"