@Weren: Didn't really think that was possible. Nice to hear though. Maybe I can make it this time as well.
@Xant: The whole thing about becoming the evil's puppet isn't all so foreign an idea to me, because Geralt does lots of things just to survive and get himself out of messy situations. This was just one of those situations. And I said, I believe Geralt already knows there is more to O'dimm than meets the eye.
The actual stupid event occurred when Geralt didn't act rationally enough, and did a tremendously stupid thing as even letting Shani be nearby a necromancy fest instead. In fact, it was equally stupid to see Shani roaming dark underground tunnels full of corpses done in by such a dangerous creatures as the Toad Prince when you first met her. I guess it would make better sense, if Shani wasn't essentially involved with the possession.
Also, on another note, I can't help but wonder. How is it so easy for a random spirit to possess Geralt anyway? He couldn't even prevent it.