I just tried hide and seek with Max again, and he was scary! Why would a dog react aggressively to hide and seek?

My husband did it last week - hid in the guest room and Max wouldn't let him out! As soon as Max found him he started barking and growling, and he literally wouldn't let Bob out of the guest room until I came! Bob and Max get along great, and Max obeys Bob well. Max is usually a very sweet dog and not at all dominant.

Today I tried it - I stood up and covered myself with a blanket. Max jumped up and put his feet on my shoulders and grabbed the blanket off my face with his teeth and tried to chew it up.

Wierd, huh?