Ivar is indeed left breathless by the siren's ways. He's not all that experienced sexually, so every experience always turns out being blissfully new and wonderful for him. One hand comes up to run his hand over the muscles of Llŷr's chest, while the other still holds onto the blade.

He runs the tip of his knife lightly over the skin of Llŷr's powerful shoulders and collarbone. Ivar is tempted to cut into the skin and see a bit of blood, but he refrains for two reasons. He's not nearly so cruel as all that while he's under the chalice's effect and he knows threatening the water spirit will only provoke him into start singing again. This time, Ivar might not be able to stop him.

Though the way things are going, he might not want him to.