Can anyone explain this?

My husband and I have recently discovered I’m fantastic at hand jobs lol 😂 tmi but he shakes and shudders the whole time. It’s amazing lol but my question is when he cums if i keep stroking it he can’t hold still. he says it feels too intense. Like it feels good but too good, to the point that he can’t take it anymore kind of thing.

Does anyone know anything about this? I tried googling but couldn’t find anything.

I’m curious as to what causes this and why, and if it’s normal for men.