every house has gas heat/stoves & the hero instinctively knows not only how to turn the whole house into a giant bomb, but also the exact amount of time it will take for the house to fill with gas, thus enabling him/her to use the appropriate makeshift fuse that is timed to blow up the housebomb at the precise moment that a) the villian(s) set foot inside, or b) the exact moment that one of the villians realize that the a trap has been set