There's a silent look of agreement. The Doctor himself would have said, 'Thar's truth in legends' If someone wasn't concealing themselves.

"Oh come on. You telling me you believe in magic? Really? Really?" The Doctor makes a face, rather baffled. That's not something he expected The Master to have faith in, if someone had faith at all.

However, given the possibilities of this place and the multiverse. The Doctor has subjected that magic is possible by math - somewhere.