Glad you found the culprit. The only good news about giving them hairball medicine is that they actually like it. Tubby used to just lick it right out of the tube. Peanut, however, never really like the stuff so one time I tried putting it on her paw so she'd have to lick it off. Weeeeelllll.....not a good idea since the very first thing she did was flip her paw and I then had nice brown, sticky hairball stuff all over my white walls.