He paused in front of her cell, looking in silence for a full minute before finally asking, "Don't tell me. Lost a bet?"

She followed the direction of his gaze. "Nope."

"Obscure alien tradition?" he tried again.

She looked back up at him. "Nope," she repeated.

"Fashion statement?"

She chuckled. "No."

He thought for another full minute. "Out of paper?" he suggested lamely.

Her chuckle turned into a full laugh but she shook her head.

"What then?" he asked, finally giving up.

Doctor Song glanced back down at the black tick marks covering every inch of her exposed skin before looking back up at him. Smiling brilliantly, she explained, "It's April the first again."