How do you get a mouse out of an air duct?

Answer 1

You could catch it with a normal snap trap that kills mice. Or, if you prefer not to kill the mouse, but just to remove it, you can buy any one of a variety of live mouse traps that catch the mouse without hurting it, like this one:
http://www.abundantearth.com/store/mousetrap1.html If it is a normal house mouse, though, I suggest that you do not release it since they are an exotic species to North America. Most mice that cohabitate with humans are house mice (Mus musculus) and can be recognized by being smaller than most wild mice with a tail about as long as their body and a nondescript grayish-brown color.