Mark the frame where the animal starts doing something different

There is no right label and no list to choose from. Watch each clip and mark every frame where the animal starts doing something different from what it was doing. If nothing changes in a clip, say so — that is an answer, not a skip.

Your clips come in an order of your own, and your marks are saved in this browser as you go — you can close the tab and come back. This site has no server, so nothing reaches anyone until you export: press Export my marks and send the file on.

Why it is worth doing: a detector was scored against planted boundaries and found 12.8% of them, but the plant turned out to be a far easier target than a real boundary. People agree about when something changed far better than about what it was, and that agreement is the only benchmark this question has. Two raters are the minimum; one gives no benchmark at all.