'The Bird Undertaker' by Cassandra
When he sees her, she's holding a funeral for a chaffinch. It died of cold, she tells him, patting the soil. They can't store fat. It weighs them down. Captivated, he suggests hot chocolate; when she counter-proposes sex, he's lost.
Her appeal's distinctly avian - small bones, quick movements, bright eyes, sharp little face. Three years later, she kills him (I've met someone else, I'm leaving now, bye.) Lying on the kitchen floor, all the blood leaking out of his warm mammalian heart, he longs to shed his coat of fat and fly after her, tearing her to shreds with his talons.