Do Not Disturb

I've noticed lately the Doctor never seems to pay attention to anything but what he's currently doing. He says it's because he can only concentrate on one thing at a time. Also, when I ask if I can help, he often says "Yes", but when I ask how, he says, "Leave me alone", like he did to Sarah in "The Invasion Of The Dinosaurs". It's rather strange, the things he says sometimes. For instance, he was working on something, and came in and said "Hello." He didn't look up from his work, but growled, "Don't hello me", in that "I'm busy. Go away" tone. I was in a very mischievous mood, so I broke into an evil grin, giggled naughtily, and said, "Hi!" Now, I expected him to say "I said, "Don't hello me"! I'm busy!" but instead, he calmly replied, "That's better." But what's really funny about it, is that he meant it! He had no idea why I laughed!