Knock knock. Who's there? Canoe.

Canoe who? Canoe let me in, it's freezing out here!

Knock knock. Who's there? Amos.

Amos who? Amos *astounding* fact about puns is that Amos *clever* one is Amos *likely* to make you *a-moan*!

Knock knock. Who's there? Cows go.

Cows go who? No, cows go 'moo'.

Knock knock. Who's there? Homer.

Homer who? Homer-ly, who could resist a classic like this? It's an *epic* pun, don't you think?