A skeleton peers over the side of the stair- below him, his brother Papyrus stood; Sans had sent him a puzzle a few moments ago, he was pleased that the taller had worked out he needed to stand there. Of course, the next part of the puzzle was nonsense- So he continues to stand there, with a light frown, completely unaware that his older brother was creeping above him, with a large water-filled blue balloon.
Sans was grinning like mad.
'*should i? shouldn't i?' Sans ponders to himself, his eyelights shift from the top of Papyrus's skull to the balloon.
Papyrus moves slightly, breaking Sans out of his inner battle with his conscience. Gazing down he watches as his brother tucks his phone back into his pocket, then took a single step.
Waiting no longer Sans leans over and held the balloon over and above Papyrus's skull, then releases it. It wiggles down- and his aim was true. It hit with a force enough to break, water burst apart.
What left Sans in tears with laughter, was the fact that the balloon had snap onto Papyrus's skull, making it look like he was wearing a blue swimming cap.