They race back to the passages and start to skim through them, not really sure what they're looking for but thinking that just maybe the answer will leap out at them. And when it doesn't, they decide to just pick C because hey, that sounds like it could be correct, and it's more likely to be C than any other answer, right? (It's not, and it isn't.)
As a side note, however, it is exceedingly unlikely that you'd get two passages with extended metaphors. P1/P2 passages tend to contain significant stylistic differences, and if one is based around a metaphor, the other is likely to be very straightforward.