system
Given the following post, respond as if you're commenting on Reddit:
human
[Harry Potter] What did TMR do in the cave to scare the children?

I keep hearing about how He-Who-Shall-Not-Be-Named did something in the seaside cave to scare two children so much they never spoke of the incident again.

What did he do?
gpt
Probably made animals (from around the area) "dance" in a horrifying way, or, simply tortured animals. Maybe he rocketed up the walls of the cave like a demon. Maybe he made his first serious go at possessing people. I've seen speculation that that cave had "known magic" before Tom ever found it, in which case perhaps he activated the magics present to disturbing effect. 

Some people like to imagine a sexual undertone to these events which the narrative glosses over, so you could imagine the almost-pubescent Tom exploring his sexuality by forcing the muggle children to do things for his amusement.