curious question

I have a 6 and a half month old cat and lately he has been holding his mouth slightly open like a dog with his tonge slighty out, almost as if he is thirsty. What could this be, most likely nothing, i mean it is nothing that anyone would notice if they are not around him, but I am a very protected owner and was just curious.

our cat used to do that when she was little..she only did it when she played fetch for too long. She loves to play fetch so if we keep throwing her toy, she will keep chasing it even if she gets tired. When her little tongue would stick out and she started panting, we knew we had to give her a break..

So, for our cat it was just exhaustion that caused that..Once she settled down, the tongue went back in and she didn't pant anymore.

Is your cat playing too much to make himself too tired maybe?

Cats do pant, just not frequently.

What I think you may be seeing is your kitty using his Jacobsen's organ, another olfactory sense located in the roof of the mouth in the palate.
It's somewhat keener than the sense of smell alone and with it, they can gather a lot of information about a particular smell.