Maybe you’re thinking of “snapper.”
From: Mark Twain Forum <[log in to unmask]> on behalf of Clay Shannon <[log in to unmask]>
Sent: Thursday, May 4, 2023 5:07 PM
To: [log in to unmask] <[log in to unmask]>
Subject: Lightning/bug

Twain used a certain word for the part of a story that caused a jolt to the reader or that made them laugh. He didn't use the word "punchline" for this; does anybody remember what it was?

-- B. Clay Shannon