Because he was under cover.
or
I said, "I've been on telly but I'm no Dean Martin".
or
When it came time to pay, the skunk didn't have a scent, the deer didn't have a buck so they put the meal on the duck's bill.
or
I thought, "He's trying to pull a fast one".
or
They turn from notating nuclear spins to notating unclear puns.
or