"Slide down the drain-pipe, onto the kitchen floor, and we'll be, friends forevermore!" The Doctor ended on a shout while Donna trailed into laughter, but the rhythm of their hands clapping together didn't falter.
"No one's supposed to be able to learn those past the age of six," Donna pointed out.
"I’m a prodigy," the Doctor assured her, rubbing his hands together as though his palms were still stinging.
"Teach me one of yours, then," Donna said.
The Doctor hesitated, so long she thought he was going to refuse or change the subject, but finally he said, "Ours were... complicated."