Errr, good point.

Of course, for all I know it wants to be drunk. If that is the case then who am I to go about projecting my mind and other optimising?

The animal staggered to its feet. It gave a mellow gurgle. 'A very wise choice, sir, if I may say so. Very good,' it said, 'I'll just nip off and shoot myself.'

He turned and gave a friendly wink to Arthur. 'Don't worry, sir,' he said, 'I'll be very humane.'

How much intelligence does it take to know when something weird is going to happen?

About as much as it takes to detect a sudden involuntary contraption of the throat muscles, combined with a jolt of various hormones and a few other such symptoms.

So, probably not much more than a polygraph. Plus whatever intelligence may or may not be required to look into the future.

(Forgive me if people already discussed all this and just I didn't see it.)

Where is the intelligence located?

Well, we know a person can appear to turn into a cat. One could probably take this as evidence for wizards' ability to fit a time-traveling intelligence into a can of soda. But it seems to me that the simplest explanation for both (or the one with the greatest prior probability) involves a Source of Magic teleporting in a newly made cat body that it controls using the memories and personality traits it finds in the human body it just snatched. Then this intelligence 'writes' the changes to the original body or a copy. So the good news is, you probably don't have to worry about the soda and wizards seem halfway to a form of immortality.

Obviously this has disturbing implications as well. The fact that Harry's world still exists seems like a good sign, as does the existence of time-turners if that really rules out a standard simulation. But the fact that "the Universe wants you to say 'Wingardium Leviosa'," suggests an imperfectly-Friendly AI that cares about a dubious form of volition among people with a certain genetic marker.