I did 4 of my dogs nails last night. I cut two nails too short on one of the dogs... I have a gel that stops the bleeding instantly, but I'm sure it still hurts the dog.
For those who have dogs that freak out, have you tried a sturdy file/emery board? They even sell them for dogs - one came with my nail clipper. Also, make sure the clipper is sharp and doesn't make noise cause that scares them, too.