“When Sky is copying people’s speech patterns, we both had to learn the square root of pi to two or three dozen decimal places, but it was almost impossible to keep up with David. His speech pattern, the rate at which he speaks, is phenomenally fast. Really, really quick. He learns pages and pages and pages. And the rate at which he speaks is the rate at which he thinks. Russell explained to me that David’s Doctor has a lot to say, because that’s David. He’s so bright. Isn’t that brilliant though? The things that Russell thinks about and then re-interprets - I think they’re both amazing.”
– from DWM #397
From the Midnight DVD Commentary (with David Tennant, Russell T. Davies, and director Alice Troughton):
David Tennant: We did rehearse the pi-number quite a lot…
Russell T. Davies: I remember you learning that the day after you got the script!
DT: Yeah, I just thought, “Oh, I see…”
RTD: You walked into the Sontaran read-though and just rattled off the square root of pi!
DT: I got the script the night before, and thought, “He’s given me the square root of pi to 30 decimal places… I’m gonna show him.”
RTD & Alice Troughton: [big laugh]
DT: …and I got up early, and learnt it over breakfast
RTD: And it was brilliant!