I don't understand this

A teacher asked her junior class to names things ending in “tor” that
ate things.

The first little boy said, “Alligator”.

“Very good James, that’s a big word”, said the teacher.

The second little boy said, “Predator”.

“Yes, that’s another big word”, said the teacher.

Little Johnny says, “Vibrator”.

After nearly falling off her chair, the teacher says, “That’s a big word
Johnny, but it doesn’t eat anything”.


Well my sister says that hers doesn’t half eat batteries!

Naughty, naughty, LOL. Good one!