Its actually a common thing with shows involving alligators because of where their eyes are (i think im not actually sure) if you put your arm in they wont be able to see it so they wont snap shut. unfortunately for him he did it wrong.
The guy survives, but he loses his arm. It turns out that particular crocodile wasn't as trained as the others in the place.
In fact, it was the first time the guy was gonna try out the trick on him, but I don't quite understand why you would perform a first-time stunt on an untrained crocodile in front of a large audience.