Something Smells Fishy

Towards the end of the movie, with the final battle with the monsters, they enter a cave and Jack says, "Smells like methane." Well, no it doesn't. Methane is the main component of natural gas (~97%), and is odorless. Only when you add mercaptan (odorant) to natural gas does it have a scent simlar to rotten eggs. He might of well said it tastes like air.