Yes you can burn it. C4 needs a fairly deliberate effort to explode. There have been issues where improperly set large shots of C4 end up on fire all over the area rather than exploding. Which is a suboptimal situation.
For eating, the way I heard is that people would stick a piece inside their lip ala a tobacco dip. Supposedly the contact with the inner lip causes some kind of heightened feeling. I can’t prove that one though.