Axolotl opening and closing mouth?

I forgot to ask about this when it happened, and today he did it again so here's the story.

So one morning I came down to eat breakfast, I look over at Marlon's tank and he was staring at me. I stared back at him and he opens and closes his mouth?? He did it a couple times maybe every 5 minutes until I went over to see what was up, and then he stopped.

Was it to get attention? He doesn't do it when I'm looking directly at him. Or is there something wrong?

I managed to get a video of it, only once right at the beginning of the video, you probably will have to replay it a couple times.

Oh and I removed the rocks, I got worried he might swallow one so he's got a barebottom tank now, hopefully he will adjust. I cannot tell the water parameters yet, I will go out and find a testing kit this weekend if I can.

Can anyone explain this behavior??

Here.

Perhaps he's got a pebble stuck in his mouth.......they are totally unsuitable for axolotl....use only play sand or bare bottom...if he hasn't swallowed one yet...he soon will.

Yeah, he lived with these pebbles all his life, I'm scared that he's been eating and passing them the whole time. They are gone forever now though.

I did manage to look inside a couple times when he opened it today, but doesn't look like there's anything in there. Hard to tell for sure though. I'm not too into forcefully looking either, he doesn't really like being touched.