Hope I am posting this correctly and not reposting someone elses hint.
I have had a few villagers bonked on the head by coconuts and then they get stupid and their name is automatically changed to " ? ". the first wasn't recovering and was just wandering around being stupid. Well after this happened a second time I changed the villagers name to stupid. what do ya know they made a full recovery almost immediatly. So I went and changed the first ones name to stupid1 and it was a miracle.

Here is a complete list of island events, including that one. Enjoy!

That list is not complete, and is only what one person encountered while playing. Some events have unpredictable outcomes, as well, so they are different each time they occur.