In the seventh-season episode of Star Trek: The Next Generation titled “Attached”, Picard and Dr. Crusher are being held captive on a planet. During an escape attempt, they are in a series of caverns when Beverly says, “I smell gas” and there is an eruption of flame from the ground a few feet from where they’re standing.
Problem: natural gas has no smell. That rotten-egg smell usually associated with natural gas is added by your local gas company so you will notice a leak. There is no logical reason for her to say “I smell gas”, because she couldn’t have. There might be a possible exception if the gas in question is propane, but that smell might be added as well.