A phantom shit is the rare phenominon wherein a shit (usually of a solid, well-defined mars bar-like constitution) disappears entirely from sight before the shitee has a chance to admire his creation. A phantom shit completely submerges itself beneath the upper waters of a toilet-bowl in an instant.
Initially such an occurence brings on the sensation of euphoria. However, the bliss is quickly replaced by paranoia and self-doubt as one tries to recall if they did truly shit or not. Usually the doubt can be subdued by wiping ones ass and finding shit upon the toilet paper. However, if the shit was a clean run and the toilet paper produces no shit-stains, then symptons may intensify until the shitee becomes a paranoid retard who believes in, and creates, conspiracy theories.