You can buy a product from www.bugspray.com to counteract dead animal smells. (happens to pest control once in a while). Also, you might do an internet search for a dryer vent brush. These are 4" diameter brushes with a flexible extension that allows small ducts to be swept clean. Also, you might try using a shop-vac. Just feed the hose into the vent pipe and keep going until the sound of the motor increases indicating you caught one, then reel it in. You can hook together several flexible vacuum hoses to get more reach if needed, but I recommend you tape them to prevent loss.