Harry always noticed one small detail in his soulmate: the fangs. Those sharp, dangerous fangs he felt at his neck. It's only a tease, not a bite, but he knows he wants that risk.
A firm grip on his hair throws his head back and a shiver runs through Harry body at the temptation as those fangs nibble at his sensitive skin. A sound involuntarily escapes his lips and he presses himself against the chest on whose lap he sits, his fingers trying to hold on to the robe.
He could have sworn he felt the smirk on his neck before his fangs dug into his skin until it bled and the venom that entered his veins made his veins itch with pleasure. Harry cannot keep a moan from his lips, and cannot focus on anything but this feeling, these fangs that drink his blood.
His eyes squeeze shut, this is such an intense feeling. He can't realize that his body is shaking. It seems to him that if things continue like this, he will shamefully go over the edge, and if it happens, his soulmate will never leave harry alone. He simply cannot allow his little kink to become known.