I'm intrigued by the "split-tail" siren image. In the more commonly seen type of image, the mermaid's transition from human to fish begins at her waist, meaning she would most likely have fish genitalia. The split-tail version would likely have human genitalia. The implication is that a horny sailor could have sex with the split-tail siren in a normal fashion, whereas having sex with the more conventionally seen type of mermaid pretty much equates to fucking fish.