Quote Originally Posted by JKExotics View Post
Co2 will not work on small rodents, dry ice can burn skin. Dipping into water is cruel if you ask me and quite unnecessary. Simply put it in a small bag and put it in the freezer 30-45mins later job done.
Well it's doesn't seem to be much different.. Dip it in water, it freezes and dies, probably quicker then if it was dry..

That would be the only away unless you want to do it yourself:

For me the below would be the fastest, just not sure how small it is.

Cervical dislocation, dislocation of the neck, is a simple and humane method of killing mice and small rats (<125 gms). Although not required, the use of sedation or anesthesia prior to euthanasia is encouraged. If sedation or anesthesia prior to cervical dislocation is not used the investigator must provide scientific justification for its exclusion. In the case of mice and small rats, the animal is held by its tail and placed on a surface that it can grip, then it will stretch itself out so that a pencil or similar object can be placed firmly across the back of the neck. A sharp pull on the base of the tail will then dislocate the neck.

From: http://research.uiowa.edu/animal/?get=euthanasia