Interesting thing about the grunt w/ no mask. Maybe a melee to the face of a grunt will knock their mask off, making them unable to breathe. That way, instead of just dying instantly, they'd lay there on the ground suffocating and screaming all sorts of hilarious grunty things. As far as them breathing methane, it would depend on what percent methane their atmosphere is. Oxygen is a highly flammable gas, but since our atmosphere is only 20% oxygen it's not a problem. If we had a 100% oxygen atmosphere, THAT would be a problem. Same thing applies w/ methane I believe.