It is hard to explain because this happen in a lot of situation.
The most disturbing i see it's somebody activated a landmine without crouching, so i didn't know that what he was doing and i walk on it.
(yeah sad for me and good for him^^)
It's also happen when you are lying and try to eat or drink and you character stand up.
Another one it's when you crouch and search for stone the character stand up but if you stand up and search for stone he crouch.