The Whole Dog Journal article "What Does It Mean When My Dog Smacks His Lips? Common Causes and What to Do" says that lip smacking is often normal around food. Dr. Lori Teller, a veterinarian and clinical professor at Texas A&M University, says a dog may drool and lick its lips when it smells food. She adds that dogs may also lick or smack their lips after eating to clear crumbs or water droplets.
Persistent lip smacking can signal a problem. Dr. Carly Fox, a senior veterinarian in the Emergency and Critical Care Service at the Schwarzman Animal Medical Center in New York City, says a veterinary visit is recommended if the behavior is repetitive and comes with inappetence, vomiting, pawing, or excessive drooling. Fox also says that, rarely, dogs with facial seizures may repeatedly lick or smack their lips during an episode, and these dogs are typically mentally altered as well.
The article lists other possible causes. Nausea is one of the top reasons a dog may continually smack its lips, according to the article. Anxiety and stress can also cause the behavior. Dr. Teller says dogs may smack their lips at the veterinarian or during th