What is in this birds mouth?

Watching a doco and this bird fed it's chick and this thing came out of its mouth, then the bird sucked it back in? Benedryl Cucumber didn't say anything about it, but I need to know if it's food or bird or something else. He also didn't mention the bird species, but it is on an island in the south pacific if that helps/matters.

Anyone know?

Also, sorry if this is the wrong place, went to a couple other subs that ultimately led me here and this felt the most appropriate.