On a hunt to find a longer video, I am reading youtube comments saying: guinea pig instinct is the need to be constantly aware of predators, and alert other guinea pigs in the area, and so they do sleep with 1 or both eyes open, unless they feel 100% safe.
I might have been a guinea pig in another life.
Ha! In my head I first thought disney, and was singing “the cold water never bothered me anyway 🎵”.