"N--" Andrew starts to answer the Doctor first, since it's a quick question to answer. Before he's even done with the first consonant, though, he realizes that saying it would be as good as telling the Doctor who where he'd come from. He freezes up, giving the Time Lord a look akin to a deer in the headlights of a car as his mind races to find a way out of saying it that won't end in the Doctor just finding out from someone else anyway.

"I'm Andrew because it's a perfectly nice name and I needed one that was just mine," he says too rapidly, turning all his attention back to the pony and squarely ignoring the Doctor.