2nd switch (spoiler)

Someone else brought up this point, which hadn't occurred to me at all.

Why do they make a point of explaining that there's a second switch "in case the first one fails"? Seems unlikely that a switch would fail in what must be a pretty simple piece of circuitry, and adding a second one would make it unnecessarily complicated. Did they want to give us the succour of thinking that perhaps the bomb didn't go off after all?



I think we're the green thingy.