And now, it's time for gratuitous violence against plumbing fixtures. Somewhere, the Wild Dada Ducks are crying. What Liam's doing is testing the theory that the killer flushed his or her excess dry ice down the toilet. He explains, "When the ice was flushed, it would have lodged in the drain trap. As the ice sublimated, gas was released. It would have built up, causing the toilet to explode." As the toilet bubbles and squeaks, Sara shares the news that Zach's alibi checks out, so he's officially off the roster. Liam sighs that he had the dorm's credit card records checked; nobody in the dorm bought dry ice on credit, and when he checked retail outlets, nobody had purchased a large quantity of dry ice in the last few weeks.
Cue the toilet exploding. Both Sara and Liam crack up from the sheer joy associated with having blowed stuff up real good. The explosion jars Sara's brain, because she suddenly realizes, "We are talking about a university here. Science Department would probably keep the stuff on hand. Science major would have access." SCIENCE DEPARTMENT? SCIENCE MAJOR? Which science discipline? Which science major? I used to date a chemist -- he had access to far different lab materials than I did as a microbiology student. You'd think that geeky Sara and geeky Liam could have name-checked a few disciplines which use dry ice.