[poorelise]

Reminds me of Comed-Tea in "Harry Potter And The Methods Of Rationality":

"If you drink it, something surprising is bound to happen which makes you spill it on yourself or someone else. But it's charmed to vanish just a few seconds later"

[eli_gottlieb]

Except of course, that was done via a cheap trick with minor prescience: the tea transmits an urge to drink into your mind when it detects that something funny is about to happen.

[poorelise]

You might want to add a spoiler warning to that, as the actual mechanism behind it is not immediately revealed in the story :-)

Still, I don't see why the Predictor couldn't work in the same way - how would you determine that it doesn't?