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Dogs generally lick the floor when they're feeling nauseated.
However, they can also develop an obsessive-compulsive behavior of floor licking if they don't have enough exercise or entertainment during the day.
If this were my pup, I'd have his regular vet take a peek at him, just to rule out any possible medical problems. If that comes up clean, then it'll be time to work on modifying the behavior.
I hope this helps.