Choo-choo train sound

TOOT

Think of the short, playful horn sound a conductor might make when pulling out of a tiny station in a cartoon.

The clue "Choo-choo train sound" plays on the familiar onomatopoeia for a train whistle or horn, which is often written as "toot-toot" in comics or kids' media. While "choo-choo" mimics the chugging sound of a train moving, the actual horn sound is a sharp "toot," making that the answer. It’s a straightforward example where the clue hints at a sound effect rather than a literal word. Think of cartoon trains blowing their horns—what noise do they make?