I see people insert their hand at the gap of closing lift door to make it open back. They obviously don't realise sensors can malfunction and the door might trap their hand. Then the lift car moves....

You forgot the one which got SF Bora-ed.

And hopefully they won't be harassed or be repeatedly reminded of this by their own parents.

People tend to underestimate the force of closing lift doors. I realise mechanical sensor (the moving piece) imo is more predictable compared to electronic sensor (infra red or radar? type). If you push the mechanical sensor and the door doesn't stop (unlikely), it means it won't stop and you'd better gtfo. IR sensor, meanwhile, is a lot more hard to predict.

I was having the same thought. Or maybe he didn't realise the lift car can do that to him (kids mah).