Shame you ought to feed them , they be hungry.

There is probably some mould growing below the plaster that is smelling appetizing to him. Spray the wall area with bleach, I think it will kill the smell & the mould.

Maybe he has toothache or is looking for a cure to his bellyache. The paint and plaster will not do him any good.

The last time I saw my exhusband doing this they carried him away in a straight jacket.

Couldn't resist adding : He must have heard the old ice cream advert "Don't you know..WALL's have all the fun flavours"

Your dog has a mineral deficiency, take him to the vet immediately.

Maybe he hates the colour of the paint.

Must be lacking something in his diet.......

Hehe @ Robin and Boerseun. I think Snowdrop's answer is probably the closest to the problem.