Thanks, folks! I volunteer at the county pound and talked to someone today about them, too. He recommended some Robitussin DM and wait it out a bit. I attempted just 1.0 ml of it on the Chihuahua and haven't noticed any difference. The good news is that it doesn't seem to bother them during other physical activity. We've been on walks outside (I live in AZ, so it's nice out) and he just hopped off the treadmill, too. The coughing only seems to be a problem when they are playing with each other. I'll call my vet tomorrow and see if he wants to see any of them. Just wanted to get everyone's opinion, but it sounds like everyone agrees on KC, so thanks!