I was an occasional hider.
Usually when I didn't want to go someplace.
Or didn't want to leave the place we'd gone to.
Purposeful hiding.
I used to babysit an evil child who used to hide so that he could lure you into a room - and lock you into it.
Purposeful hiding.
He stopped after I climbed out the window and caught up with him in the house.
I didn't do anything to him, but he didn't know I wasn't going to.
Several of my friends' kids have gone through bouts of hiding. There usually seemed to be some kind of purpose - very individualized purpose.
Wonder what Mo's purpose is. Confirmation that you'll look? Confirmation that you won't get mad? Trying to stay where he is? Trying to avoid going somewhere/doing something? ...
How long has the hiding been going on? It might be a brief, horribly annoying interlude.