I have a 6 yr old cocker spaniel. Today out of the blue as I was walking him, on the lead, he really went for another dog who was walking past. The other dog did nothing to provoke him, my dog just jumped on him and started having a go. He must have tried to bite it too as he had hair round his mouth. I was in total shock as he has not done this before! He sometimes growls abit if a dog sniffs his nether regions ( a dog did bit him there once so he is bit funny about it), but never this. I could only apologise to the owner as was dumsbstruck....what should I do, why did he do it?