Dogs lower jaw trembling and quivering

[Littledogball]

My little dog has just started doing a really weird thing with his lower jaw, I'm not sure he can help it actually. His lower jaw does this weird quivering or trembling for about 2-3 seconds and then it stops.
He seems fine in himself. He is old, 13, he doesn't seem to be in any pain.
Any ideas?

Context is quite important.

Some dogs do this when they smell another dogs urine, or something they like the smell of - you see their teeth sort of chattering. It is called the Flehem response

However if it continues or your dog has not been sniffing something it can be a sign of pain of discomfort.

He does it after he's eaten or been for a walk. He sleeps a lot so it's hard to mail it down as to when as he doesn't often toddle about.

If it's after specific activities I would worry about pain - at his age it's probably best to get him checked by a vet.

Example of the flehmen response here - for comparison.

(though it can also sometimes look like an upper lip curl or licking, depending on the dog's habit)

One of my terriers used to do this if he got excited by something.

He doesn't seem in pain? He's a bit stiff sometimes I think

No, it's not this. It's his lower jaw trembling

Dogs hide pain really well - generally by the time they're showing symptoms the problem is quite painful.

Please get your dog checked by a vet - especially as you say he's stiff. Anti-inflammatories and supplements could make the world of difference.

It could be dental pain.

They hide pain very well. Our old westie started shaking a bit and it turned out he was in pain in his hips. I would get him good joint supplement and vets full check up.

I will do that, thank you