In WWII the Norwegian underground notified that the entire sardine catch had been purchased by the Germans and ordered to be shipped to their U-Boat bases. They assumed that the canned sardines would be used as food for U-boats and asked if the OSS could provide something appropriate to put in the cans.
The OSS sent Croton Oil, a very powerful laxative that they believed would be undetected in the strong taste of the sardines and their preservative oil. You can only imagine what it would be like on a U-boat where the whole crew had a severe case of the runs. But the OSS never found out if its sabotage had worked. Maybe some U-boats foundered due to excessive use of the toilet, or maybe the Germans just threw the stuff overboard.