Paddy always flinches if someone he doesn't know very well comes at him head on with hands outstretched. If he's off-lead, he just dodges away. If he's on lead, he flinches and looks worried.
The difference is that, on lead, a dog has fewer options to choose a reaction from - he can't run away if he's scared - so is more likely to escalate to a growl or a snarl and snap - in Zack's case, this "imprisoned" reaction would have been exacerbated by having the ear infection.
poor dog - hope he's better soon.
Denise