In relation to rats: When rats brux (grind their teeth) they often do it with such force that the jaw muscles cause the eyeball to vibrate in its socket. This can appear as just a small wiggling of the eyes, but occasionally the eyes will appear to pop in and out of their sockets. Rats often tend to close their eyes slightly when bruxing, which emphasizes the effect by forcing the eyelids to open and shut.

While often disturbing to watch, boggling is generally a sign of extreme contentment.

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