Bunny doing weird motion? Pls give advice?

[bunbunadri]

I recorded a vid of my bunny flopping and when I looked at it I saw a weird movement? He was like sucking his tummy in quickly or something like that. Pls let me know if u have any ideas on why my bunny did that? I'm kinda worried. Thanks (video)

 

[JBun]

It just looks like maybe twitching of the stomach muscles as he was adjusting to get comfortable. If there was anything wrong or something painful, I doubt he would be flopping down to relax like that.