Doesn't Clark know, from what he's seen in the musuem and the family records, that he and Lois don't die in their fifties? If so, he'll know that, whatever happens, it isn't fatal to either of them.
I figure, first, that he hasn't had time to read everything in the museum (departure room, anyone?). And second, even if he had read that he died at the age of 97, I can see him trying *not* to remember that, and therefore when Silas starts fumbling around he doesn't immediately realize it can't be fatal. After all, he's only human
PJ
