Which Came First? explained

Which Came First? implies most of its comedy. Here's a list of the horrors it implies, in case you missed some.
First implication: Spilight sexings. He gets her drunk, and she doesn't say no. (Spike/Twilight colored egg)
Second implication: Spilight eggchild. Ponies lay eggs when sexed by dragons. (Spike/Twilight colored egg)
Third implication: Celestia is Spike's mother. ("my grandchild")
Fourth implication: At some point in the past, Celestia sexed a dragon. ("my grandchild")
Sixth implication: Rarity is preparing a nest for potentially laying an egg with Spike (Final line)
Fifth implication: Rarity is showing, and is already preggers with an egg. (convo with FS)