You're a clueless parent if you're not well aware of what will scare your kid.
I'm a father of twin boys who are 17 now.
I knew very well what would scare them to what degree when they were younger.
I knew how they would react if they did get scared, and I knew how to handle them if they did.
Judging by your avatar, you seem like you're in great shape being the father of 17 year olds.