A few months ago, we found a small, hard lump on the dog's left side of his neck, he was about 9 months old at the time. It didn't seem to bother him and there was no change in his behavior or eating habits. His favorite activity is going to the dog park, where he is the youngest and most active, he loves playing with the other dogs but they all get rather rambunctious playing and "mouthing each other in their play". So, we thought one of the dog might have scratched or bitten him there. Now, a few months later, the lump has gotten bigger and feels soft and pliable, what can it be? Cause for worry?