Boy and his cat.

Spike is quite used to D crawling up to him and whacking him with his hand or whatever he's holding at the time. He puts up with it - we wouldn't get away with it, but he seems to know that D doesn't have full control of his movements yet. This time D crawled up and just looked at him. So Spike decided to get in first and tapped his hand with his paw. Felix wouldn't have allowed D to get within reach of him, he runs when D heads his way.