When someone snickers, they laugh in a quiet or secret way, especially because they are amused by something.
Snicker is usually a light and maybe a little naughty kind of laugh.
Examples:
She snickers at the silly joke.
The kids snickered behind their teacher's back.
He snickers when he sees the funny clown.
The raccoon snickers as it steals the cookies.
The naughty elf snickers as he plays a trick on the other elves.
The little girl snickers as she watches the puppies play.