Whatever it is about monkeys on film sets, there seems to be something about them that makes crazy.
After all, they're quite intelligent and hanging around on set can be extremely boring so it makes sense that they'd go a little crazy. Now, add on top of this that said monkey has to interact with Danny DeVito in the middle of Batman Returns and it just gets worse.
So, it should come as no surprise that said monkey tried to bite his balls off - because that's exactly what happened, as DeVito described in excruciating detail to Ewan McGregor, Sam Neill and, of course, Graham Norton.
He's telling this story and, sure, we know it's on a film set, but it sounds exactly like something that'd happen to Frank Reynolds. In fact, pretty sure this was something like an episode of IASIP or something.
More to the point, why was Sam Neill crying laughing about all this? It's funny sure, but did a monkey try to nibble his off as well? Who knows.