Knock knock. Who's there? Waiter.

Waiter who? Waiter minute, I thought *I* was supposed to be asking who's there!

Knock knock. Who's there? Dew.

Dew who? Dew-n't worry, it's just a drop in.

Knock knock. Who's there? I'm not sure.

I'm not sure who? I'm not sure who is asking, can you please state your full name and the purpose of your visit?

Knock knock. Who's there? Listen.

Listen who? Listen, this isn't a joke, I just need you to open the door.