Scientists were put to the challenge of determining what a smile on a rat's face looks like. Therefore, as scientists do, they experimented with lab rats by photographing their subjects while being exposed to things that might make a rat happy or upset. They looked for facial displays of happy feelings in rats that were subjected to entertaining feelings, tickling and other gestures that a rat may enjoy and in contrast, blasts of cold air and loud music. They discovered that the rodent’s equivalent of a pleased grin is ears that are more relaxed and pinker in colour. In rats, the main findings were that ear angles were wider and more relaxed and that the colour of ears became considerably pinker. It is also thought that rats boggle and brux when they are happy. Rats naturally boggle their eyes and brux or grind their teeth to keep them from growing too long.
