Footage
Obviously, all martial arts possess the potential to be dangerous. Posting footage here is not advocacy of these techniques, nor does it suggest that this kind of practice should be taking place in your classes. It's merely a demonstration and for education purposes.
Here are a selection of techniques with some reasonable applications to them:
Practice against an aggressive opponent will produce greater results, and as such, is more dangerous. We can see how very little effort is used here to gain temporary loss of conciousness...