Rat’s eyes boggling when making sounds

READ: in my country in TV news there is a section called something like “viewer’s reports“ where tv watchers psot videos to that tv channel and they choose some videos to show in news! And this video of my Monchichi got in there too! check here in 1:58 My rat boy Monchichi bruxing when resting in a towel after swimming in river.. his eyes are bulging out when he is bruxing alot, hehe.. some rats do that as well but no idea its just cute and funny xD