This article is from the WSSF 2015 AFRMA Rat & Mouse Tales news-magazine.
Did You Know? There are 4 facial expressions to look for to see if rats are in pain—squinting eyes, nose/check flattening so there is no crease between the cheek and whisker bed, ear changes (fold, curl, angle forwards or outwards, resulting in a pointed shape), and whisker changes (whiskers move forward away from the face and look bunched).
You can read more in
Rat Grimace Scale (RGS), The Manual.
The Rat Grimace Scale: a partially automated
method for quantifying pain in the laboratory rat via facial
expressions Mol Pain. 2011 Jul 29;7:55.