Tiger M said:
Using this line of reasoning, William Shakespeare would be considered a plagiarist.
Well, no--it was neither illegal nor considered inappropriate for early Modern authors to use plot threads, or even entire plots, developed by others.
In C21 US copyright law, there is a defense known as "scene a faire" (obligatory scene)--that is, a theme or series of events that is used so often in a genre that it cannot be considered the property of any particular writer. The fact that two detective stories include a scene in which the detective gathers all the suspects in a room to reveal the solution would be a scene a faire--and so would the ol' reliable Stranded in a Cave. I daresay that, as mentioned, Fertility Festival (with or without Aphrodisiac chaser) qualifies.
-(Y)