Our dog is 13 months old. Lovely boy but he's fearful of quite a few things, the vets being one of them. We took him when he was 7 months old for an eye infection. He growled at the vet so they muzzled him. We took him again yesterday for his booster. As soon as we went in the room he looked scared and started to growl and snarl. I put the muzzle on and he instantly calmed down. He was still scared-tail down but he let her do a full examination and injection. No growls, lip curls, nothing. I'm just interested to know the psychology of it? Does anyone know why it stopped him? Many thanks.