the_rck

We suspect the pie because it's the only thing that he ate that wasn't also eaten by someone else. The other potential culprit would be beef contamination of his food (he's extremely allergic, and no one else in the house is), but the reaction wasn't strong enough or fast enough for that, and nothing he ate was likely to be contaminated. Contamination's always possible, though, since something as trivial as a dirty pizza cutter can do it.