I've actually seen those things on the shock collars that teach dogs not to bark. My roomie had one for her dog. Mind you, the size was tiny, but the two prongs were there. It was so sad, he would bark, get shocked, and whimper because of the pain only to get shocked again. She'll have to forgive me for undermining her, but I just couldn't stand it. I would rather do my homework to barking than to the painful cries.
I took it off when she wasn't there and before she came home from work I put it back on. I did work with him on the no bark thing. At least he learned the command.