Title text:
You say no human would reply to a forum thread about Tom Bombadil by writing and editing hundreds of words of text, complete with formatting, fancy punctuation, and two separate uses of the word 'delve'. Unfortunately for both of us, you are wrong.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3126/
at that point it's just "grammar and punctuation is a sign of AI", which actually means "i don't know what AI output looks like".