The horned toad is actually a lizard, though many refer to it as a toad due to its rounded body. (Wikipedia)
Neville once had to disembowel an entire barrel full of horned toads while in detention with Snape. Afterward, Ron fantasized about Mad-Eye Moody turning Snape into a horned toad, similar to the 'amazing bouncing ferret' punishment inflicted on Draco Malfoy (GF14).
Poor Neville had quite an evening, it would seem. One can’t help but wonder why anyone would need hundreds of dead lizards, or indeed where Snape would have even found an entire barrel full of them, since they’re native to North American deserts and their population is in decline (and are considered endangered in Texas). The callous way the Wizarding world deals with animals can be very disturbing.
On the other hand, by the time Snape had him disembowel toads, the Death Eaters knew the Dark Lord was returning soon because their Dark Marks were burning. Disemboweling toads could be seen a foreshadowing Neville's future: the sweet boy who loved his pet toad, had to toughen up to face evil Bellatrix Lestrange, and indeed eventually faced a giant reptile - the horcrux snake Nagini at the Battle of Hogwarts, which he slew with the Sword of Gryffindor.