Spaceball.

It takes Mal a minute or two to winch up the rim on a chain in the center of the cargo bay.

It takes Mal even longer to arrange a carefully-placed stepladder of boxes along one side of the playing field.

The arena has been set.

Walking over to the shipboard comm, Mal calls:

"This is the captain. I need all personnel in the cargo bay."

Mal stands in the center of the field of battle and waits. Grinning.

Kaylee's Dare.

The sketchpad had pretty high quality paper in it.

This is why Mal is grimacing at the small pile of balled up pieces of it in a corner around his wastebasket.

If he's gonna make good on Kaylee's dare, he's gonna do it right, gorramit.

Picture finally done, Mal leaves his bunk and makes short work of the distance between there and Inara's shuttle. Walking in without knocking, he thrusts the piece of folded paper into Inara's confused hands without speaking.