Flash

I've always thought that flash is very dangerous, but in this shot it came out well. The girl seems surprised, did she know you were going to use the flash?

I don't know exactly what you meant by dangerous but yes it can cause quite a bit irritation especially night time. So far, I avoided a serious issue but for candid shots it has a lot potential to cause confrontation.
This shot is completely candid, she might have noticed me before the shot as I was using a relatively large camera at the eye level and I am 185cm tall.

The flash has emphasised her eyes in a strange way. Unsettling.

By dangerous I meant the "zombie effect" if not used carefully :-)