Some odd things about God of War (spoilers).

[Khuutra]

gekkokamen said:

One thing that does bother me a little is that when Kratos opens the box, Zeus is not shocked by this, or is he such a good bluffer? Zeus himself took the box to Olympus and put it inside the flame 'cause he believed there was still power inside it. It's not clear if he knew Athena had summoned Hope and locked it inside with the evils (I'd say he knew about it), but it's certain he was guarding that box 'cause there was no doubt there was power still in it.

So when the box opens again, and is empty, I think he must have thought "wtf?? then where's the power?", was his reaction to mock Kratos so quick that he didn't realize this (that the power had to be somewhere else), or did he throw an instantaneous high-roller bluff?

It would seem to suggest that Zeus didn't know it was in there - that Athena placed Hope in there in secret. Zeus may not have known he was infected with Fear, either, so it may be that he thought the evil returned to the box after Kratos killed Ares.