“Knock knock.”

“Knock who?”

“What?”

“You heard me.”

“No, come on. Knock knock.”

“Who’s there?”

“Interrupting cow.”

Silence.

A pointed look.

Silence.

“You’re supposed to say ‘interrupting cow who’ so I can–”

“MOO”

“Fine, dammit, you tell one.”

“Knock knock.”

“Who’s–”

“MOO”

“NO!”

“Did you think the cow was just going to leave?”

“This isn’t a hypothetical door-opening scenario with persistent characters! It’s a purely linguistic construct!”

“Okay.”

“Okay?”

“Okay.”

“Knock knock.”

“Who’s there?”

“The Doctor.”

“Doctor Who?”

“Yes.”

Silence.

“Get it?”

“Yyyes?”

“I thought it was funny.”

“I worked that out.”

“And anyway you already took the interrupting–”

“MOO”