What is gaping? What does a chicken yawn look like?

[Bawkbok]

Yesterday I noticed the new pullets (4 months old) opening their mouth and closing it quickly, no sound involved. They did this after they ate (greens, grass, some mash). I noticed it at other times also - not food related. Not a lot, just every once in a while. Is this a chicken yawn? Sorry no video as I can't get the phone up fast enough before it's over in a split second. Everyone is eating, drinking and acting normally otherwise. All eyes, ears and noses look good, no mites or lice no coughing or sneezing. Is this normal behavior? Thank you.

 

[nuthatched]

Likely crop adjustment

 

[CoopBoots]

Caught my Marshmallow doing this once recently in a photo. It sharts like this, followed by a little head-lift with still open mouth after. If it doesn't happen often, I don't get concerned, especially if the rest of the body posture is normal.

Edit: I'm honestly not sure if this is a yawn (do chickens actually yawn?) or simple crop adjustment. I'm here to learn, too

 

[Bawkbok]

What a pretty bird, that's a great photo!
There's usually a little bit of a head shake after the mouth open, which I forgot to mention. I assumed it was a crop thing, but they don't stretch their neck or anything as indicated in the following article. Your question - do chickens actually yawn? - led me to a google search. I guess I could have googled it first, but BYC is my first go to place with questions and the experts always reply.
Thank you.

https://poultryparade.com/why-are-my-chickens-yawning/