The important word in the question is the initial "if".
Anyone who has ever encountered a real live cat will recognise the utter impossibility of strapping anything at all to its back while it is conscious, let alone anything potentially edible like buttered bread. Therefore, the question only applies to dead/unconscious cats, which invalidates the argument. Even if you waited until it was conscious, as soon as it realised there was a slice of bread on its back, it would go completely simian excrement.