The floating napkin clearly startled him, and his reaction was simply fear. His "biting" you was also a fear bite, and not an act of aggression. Kicking him out of the garage was not an appropriate response, your dog is just fine but you need to work with familiarizing him with different things so that this doesn't happen. Get a plastic bag, or napkin, etc, throw it up into the wind, or just drop it and let it blow around. Keep him on a leash and let him slowly investigate it on his own. When he gets right up to it be like good boy! and continue walking.
Do not punish your dog for being afraid of something. A floating napkin or something like it should evoke a prey drive response--either fight or flight, and if you don't get him familiar with these things soon he's going to be a fearful hazard.
Last edited by Dr89; 12-08-2010 at 12:58 AM.