Meet new kitty, licks, smacks lips... whats it mean?

Odd behavior question... If a cat is meeting a new kitty and they kind of take a small sniff and sit a watch them. Whats does it mean/why.. They lick there lips then kind of open and close there mouth real fast, kind of as it they are smacking there lips or something..? They do that many times while observing the cat. The cat is stiff and nervously watching, and is fine unless the other cat comes to them, then its automatic gorwling hissing ready to attack. Im just wondering about the mouth thing... its strange to me, anyone know a reason or what it means?

From the sounds of it, it could be a warning to the other cat to more or less, "BACK OFF OR ELSE!!!"

I know I have seen male cats outside do something similar to this when confronting another male.

Pheonix does the lick of the lips and the 'lip smack' when she is nervous.

They are getting a sniff of the New Cat, as thier sense of smell is stronger than that of thier sight.
And the licking of the lips is a nervous gesture , probably from when they were Kittens.

Yeah, same here... my guys lick their lips when they are nervous.

The sniffing and the inhaling can be getting the scent to the part of the upper mouth called the Jacobsen's organ. They usually do that to get scent of another kitty.

Exactly, a cat does this when he is not confident. If the stress level becomes too high, it can be a sign before they attack. I could not find a better translation than "back off or else!" .