Table 1.

Behavioral states and events recorded during euthanasia. Interruptions shorter than 3 s were considered the same bout of behavior. Behavioral recording started when the gas was turned on.

Category	Behavior	Description
Duration	Stand	Up on 4 legs
	Lying	Lying down with side or sternum contact with the floor
	Locomotion	Any movement more than 2 steps, walk or run
	Inactive	Immobile, not doing any particular behavior
Latency	Ataxic	Lack of muscles coordination in basic movements, loss of balance on one or more feet
	Loss of Posture	Lying on ground and does not get back up
	Heaving Breathing	Forceful and quick repetition of flank movements, mouth closed
	Open Mouth Breathing	Jaw held open with mouth open
	Gaping	Deep forceful breath, rhythmic movements of the chest with mouth open
	Last Movement	Clinically dead, stops gaping, end of experiment time
	Paddle Bout	Rhythmic movements of one or more legs while lying
	Panic/Convulsing Bout	Erratic, uncontrolled movements including flips, flops, thrashing before loss of posture
Events	Righting Response *	Unsuccessful effort to right up on 4 legs
	Escape Attempt *	Rear on its hind legs, jump, or scratch with front legs against the walls or the floor
	Squeal *	High-pitched vocalization; extended sound of high amplitude and frequency
	Grunt *	Low-pitched vocalization; sound of low to medium amplitude.

* Behaviors recorded as events due to their brief nature, rather than as states.