Yeah - it would be pretty funny if it were true...
There's an interesting thread over on IIDB that discusses the story
Three headed frog. The thread contains an excellent dissection
of the story (see esp. pg 2), including multiple photos with annotation from different angles that pretty much calls into question the froggy mutant hypothesis. It appears that the "three-headed frog" in the story may actually be three frogs enjoying a pornographic
menage a trois amphibian moment.