Ok, I've heard of great horny toads but clawed frogs? The African Clawed Frog is kept as a pet in some states but it is banned in California because it competes with and consumes native species.
"They are really hard to pick up because they're very slippery," said Ken Howell, Asst. Curator, California Academy of Sciences. "And if you look at the back you and see the claws -- the three claws on the back there."
Nobody knows how the outlawed amphibians got into the lily pond but they have reproduced wildly threatening to wipe out most everything else. Foreign (clawed) Frogs Frighten San Francisco | 
