I watched the original video where the hot knife cuts through the lighters...and got thinking. Why don't the lighters catch fire? I mean there is flammable liquid inside of them, and they MUST catch fire, but they did not. So as I am a dedicated university student, I decided to put my science knowledge to use and get to the bottom of the question. If you are interested in what I found out, check out the video.
P.S. youtube is full of the hot knife videos....it's gotta stop hahaha