The Siren is a painting by John William Waterhouse. The painting depicts a siren sitting at the edge of a cliff, lyre in hand, staring down at a shipwrecked sailor floating in water, who in turn is staring up at her. The picture was painted in 1900 and is now part of a private collection.
https://en.wikipedia.org/wiki/The_Siren_(Waterhouse_painting)
What might a non monstrous one do their victim? Eat them still? Or some cosmic unimaginable horror?
Yeah I picture it looking like cannibalism with a disturbing amount of glee. Personally I find the idea of this nearly human creature happily devouring flesh to be quite creepy.