Is there a name for this type of sentence structure: "She looks as though she's been poured into her clothes, and forgot to say 'when'"?

Comedians seem to use phrases that employ this type of sentence structure - is there a name for it?

Examples of Groucho Marx's one liners seem to fit this pattern — and if memory serves, Emo Philips.

• One morning I shot an elephant in my pajamas, how he got in my pajamas, I don't know.

• I've had a perfectly wonderful evening, but this wasn't it.

This is called paraprosdokian.

A paraprosdokian (from Greek "παρα-", meaning "beyond" and "προσδοκία", meaning "expectation") is a figure of speech in which the latter part of a sentence or phrase is surprising or unexpected in a way that causes the reader or listener to reframe or reinterpret the first part. It is frequently used for humorous or dramatic effect, sometimes producing an anticlimax. For this reason, it is extremely popular among comedians and satirists.1

You'll find exactly the example you mentioned on the page linked above.

Here's one of my favorite examples among the many they list:

"I've had a perfectly wonderful evening, but this wasn't it." — Groucho Marx