Knock knock. Who's there? A placeholder for a name.

A placeholder for a name who? Exactly. It could be anyone, couldn't it?

Knock knock. Who's there? Disguise.

Disguise who? The sky's the limit for wordplay, so prepare for an un-pun-believable groan-fest!

Knock knock. Who's there? Elijah.

Elijah who? A light bulb just went off, I've got a brilliant idea for a joke!

Knock knock. Who's there? Isabelle.

Isabelle who? Isabelle necessary, or can I just walk right in?