Why did my dog snarl at another dog?

So I took my Airedale terrier for a walk and along the way we saw another dog and Malcolm started snarling and snapping at the other dog! He's never done that before, he's friendly with other dogs just not this one! Why would he do that?

He might be defensive, or he might have gotten into a tangle with that other dog before.

The other dog could have made a low growl that we could not hear. My Chihuahua will growl, and if his chest is on my arm I can feel it., not hear it. That must antagonise other dogs. I now watch his ears and warn him if he is causing trouble.

Maybe the dogs were sending eachother signals that you didn't see, or they were acting in a dominant way towards eachother. You need to be your dogs leader and correct him right when he does the unwanted snarling/growling. If it was 2 males, they are likely to get in a fight if they are both in a dominant state of mind or both are not neutered.Hormones often arouse fights between males and sometimes females too. A dominant dog is showing you he is the leader and is trying to take control of things! Read this link and it should really help you with your dog. http://www.cesarsway.com/By the way, I love Airedales!!