Farscape S04E10 - Coup by Clam

The crew consume food, sharing amongst themselves, unaware that if these special mollusks are not ingested by the same person, it becomes toxic. Consequently, they must quickly find a cure or they'll die. Fortunately there's someone who's happy to come through... for a price. But there's more going on here than their own problems, and solving them may be a real drag!