If Donna hadn't been there, the Doctor would've rolled his eyes at his biology. He was a Lord of Time, and yet, his bladder was never punctual. At least, not in a way that was socially convenient to him. With a small quiet sigh, he began to walk away from Donna.
"Donna, I've gotta go back to the TARDIS for just a minute," he explained vaguely.
"Why? Did you forget something?" Donna asked.
"Sort of. I've suddenly realized I need the loo, and I've never been here before.. Back in a sec," the Doctor informed her, running off. Donna shook her head at the sight of the Doctor's tight running pose.
"You didn't read any of these?" The Doctor double-checked, pointing at the spoiler-y books. Donna shook her head in annoyance.
"Riddle me this, Spaceman: why didn't you use the loo before we left?" Donna raised an eyebrow questioningly.
"Didn't need to, unfortunately," he answered, rolling his eyes obviously.
"Yeah, I think you did," Donna suggested.
"You don't double-check your body. You just wait until your bladder loudly notifies that you need to go. You could save a lot of time just by listening to your body. " she recommended.
"That..is a very good point. I may very well try that." The Doctor noted.