Ritsu's wet dream becoming true.
He knows his nii-san has a third leg.
My headcanon for MobRit is that Mob doesn't moan as he doesn't laugh or get excited, linking to his difficulty to express his feelings. But he would take Ritsu in his arms, hug him, comfort him, wiping away his tears when he's overstimulated telling him "shhhh. Everything is ok"