-You can't see it right now, but both of them have "Sow Urinal" tattooed on their back in special invisible ink.
-A sprinkler has been installed in the room that, when activated, sprays a solution that will turn this invisible tattoo visible.
-The two handleblebar-like devices that they are both holding on to are both linked to the shower of the other girl's room. If either one of them lets go, the other girl's shower will activate. (Once one shower has been activated, letting go of the other pair of handlebars will not activate the remaining shower.)
-These two girls are very close friends. They are both trying to make the other one let go of their handlebars first, so that they can sacrifice themselves for their friend.
-The doors to the rooms are not locked, and the foot restraints can be unlocked by hand.
-Just outside the room is another switch that will activate the remaining shower. Using this, the "winner" can choose to activate their own shower, and make their own tattoo visible as well. The girls do not know this yet.