The narrator relates this incident in Chapter XIV of Three Men in a Boat. George offered to cook supper one evening:
He … suggested that, with the vegetables and the remains of the cold beef and general odds and ends, we should make an Irish stew.
Such a dish is often made with leftovers from previous meals. It consists of some kind of meat, with the addition of potatoes, onions, and various vegetables. George took the lead in the cooking. Harris and the narrator were given the job of peeling and then scraping the potatoes. They weren’t good at either task, and they ended up with only four usable potatoes. To make up for the loss, the men raided their food hamper and added as many random vegetables and pieces of meat as they could find.
Even Montmorency, the fox terrier, got into the act. He brought a dead water-rat to the men, seemingly to donate it to the stew. According to the narrator, the three men devoted serious discussion to adding the rat to the mix. Harris thought it would work. George said he had never heard of putting water-rats in Irish stew, and he was against the idea. Harris answered that they could certainly try something new.
The narrator never tells us if Montmorency’s gift was used in the stew. He did admit that it “was a dish with a new flavour, with a taste like nothing else on earth.” The reader is left to decide what was really put into the pot.