The ambiguity is the lead trait. a fantasy ? memories ? an accident ? an usual event ? The answers are not useful in this case. but the cinematography, the simplicity of script, the feeling after final credits, a short film so precise than it gives a more complex story than you expect. Sure, using your imagination. A WC. Two men. An older one. Scenes not unusual. And the shadow of emotions on the face of one of characters.
