Cocoa does exactly the same thing too!! He started doing so since he was 11 weeks. (He's now about 5 and a half months.) I have no idea why he does that, but he seems to enjoy biting out the wall a lot.
He just starts right in the middle of the wall the flat surface should make it almost impossible to chew on.
I wonder if it's because he's teething or he just likes the taste.
Anyway, whenever I catch him chewing the wall, I took him away from the wall, say "No" firmly and soak the area with Bitter Apple. At first (right after I soak the area), he'd try to go back and chew the wall again, but the Bitter Apple deters him. It seems to work because Cocoa would not go back and chew on that area again even days afterwards. Of course, there are still other areas of the wall for him to chew on... I just soak the area with Bitter Apple whenever I notice that he's starting on a new area. Come to think of it, he hasn't done that for about 3 weeks now. Hopefully he's got the idea or just grew out of it soon...
