Since laughing too hard can cause involuntary urination, the Kagamine twins associate urination with laughter. And thus, even with no Rin to enjoy this laugh her body can still express the amusement… amusement at what, you ask? Why, of course at how there's no Rin to enjoy this laugh! The moment Rin pulls the trigger she's no more and instead pure fun emerges in her place. It's like Rin herself became the fun. But who is to have this fun that just was Rin? I know, let us have it while it's still warm!