Writers, what is the biggest tell that something was not written by a human?

Question for anyone who reads or edits a lot of online content.

When you read something and think "this was machine output", what tipped you off? We have our own theory list building Humanizer, repetitive sentence length, no contractions, the word "delve" used in unusual places, conclusions that summarize what you just read instead of saying something new.

Curious what your tells are. The more specific the better, we use the answers to refine our detection and rewrite logic.