If the word being said was "chocoretto" I'd say the punchline was "chekumetto". But the joke seems to not be a pun at all, just an absurd "above the expectations" situation.
Huh?Okay!TADAAAAnd now, what's this?…chocolate, chocolate…Hey Ado, say the word "chocolate" ten times.Sure.What is this setup…Is she giving me honmei choko?Chocolate, chocolate, chocolate, chocolate……chocolate, chocolate, chocolate, chocolate…T-there, I said it…?