I have had some paralyzed animals in the past and some doves and mocking birds with pox that have had to be immediately put to rest (the birds with pox would have died slowly by starvation otherwise). What we find works best with small animals is... (This more horriable than anything I could possibly say, but it works well)... we, well my husband really, puts the animal in a bag and sets it right under the car tire and quickly drives over it. It's so quick that it dies before any pain sets in. We have gassed some before, but it takes a long time and it's not easy. You need to get the gas and animal sealed tightly in a container. It's hard to get and keep the gas in a container.