Is eating grass normal or abnormal for your pet ??

Chipper aso likes to dig in the dirt and lick it sometimes. He does not do this a lot; and I don't have any idea why he does it when he does dig up the dirt. He does not do this very often, and maybe it is some kind of a mineral that his body needs more of at those times. Since he doesn't do it a lot; I don't think it is just that he likes the taste of the dirt; but that at times, his body craves something that is in the dirt.
Animals seem to just chew on strange things sometimes. Horses will chew on a tree, or even the wood in their stall. Sometimes, they do this because of a lack of nutrients; but sometimes, they just chew out of boredome when they are locked in their stall for long hours and not outside eating grass.
Horses are natural browsers; so they are designed to be doing a lot of chewing.
I don't think that it is anything to worry about if a dog occasionally chews grass, or other vegetation, as long as they don't seem sick afterwards.