"What, people call you 'The Doctor?'" Martha asked.
"Yeah," the Doctor answered.
"Well, I'm not. As far as I'm concerned, you've got to earn that title."
"Well, I'd better make a start, then." He lifted his arms and rose onto his toes, hopping into the air.
"Woah!" Martha grabbed his suit and pulled him down.
"What? What was that for?"
"The low gravity. You were starting to float away!"
"Nah, that wasn't low gravity, do you feel low gravity?" he asked as he picked up a rock and gently tossed it, catching it again. He jumped and flapped his arms once to get higher. "That's just me." He let his feet rest on the air and slowly took a few steps forward, reaching out with his hands.
"Aliens, the hospital transported to the moon, and now a flying man?" Martha muttered to herself.
The Doctor lunged and threw the rock. It flew a good distance before hitting something invisible, sending blue waves rippling outward.
"There must be some sort of forcefield keeping the air in," the Doctor said as he turned back to the balcony and floated down beside Martha.
"If that's like a bubble sealing us in, that means this is the only air we've got. What happens if it runs out?"