I understand that the urges can come suddenly when you see something. I get urges randomly like that too, and usually it is when I see something sharp and I start to think about using it as a tool. :/ It's not productive thinking and I usually try to pull myself out of it (I dissociate at some sights). Having people around you when this happens is good because they can force you back to reality and push away those thoughts before you can dwell too much.