Table 1. Original research on the grimace scale in various species.

Species	Verification method	Action unit	Decision	Reference No.
	(Type of pain elicited)
Mouse	Intraperitoneal administration of 0.9 % acetic acid	Orbital tightning, Nose bulge, Cheek bulge, Ear position and Whiker changes	Video image, Real-time	11
Rat	Intraplantar administration of Complete Freund’s adjuvant, caolin and carrageenin, Laparotomy (abdominal surgery)	Orbital tightning, Nose/Cheek flattening, Ear position and Whiker changes	Video image, Real-time	12
Rabbit	Ear tatooing	Orbital tightning, Nose bulge, Cheek bulge, Ear position and Whiker changes	Video image, Real-time	13
Piglet	Castration	Orbital tightning, Nose/Cheek bulge and Ear position	Video image	14
Cat	Spontaneous acute pain, Post-operative pain	Ear position, Orbital tightning, Muzzle tension, Whisker change and Head position	Video image, Real-time	15
Horse	Castration	Ear position, Orbital tightning, Tension above the eye area, Prominent strained chewing muscles, Mouth strained and pronounced chin and Strained nostrils and flattening of the profile	Real-time	16
Sheep	Footrot and mastitis	Orbital tightning, Cheek (masseter muscle) tightening, Ear position, Lip and Jaw profile and Nostril and Philtrum shape	Video image	17
Ferret	Telemetry device implantation	Orbital tightning, Nose bulge, Cheek bulge, Ear position and Whiker changes	Video image	18