Board Thread:General Discussion/@comment-26246605-20150513123231/@comment-26271829-20150515003900

Here's my theory:

Garnet, Amethyst, and Pearl decide it is time to see if Steven is capable of fusing with another Gem.(btw this would be far later into the show) So, Pearl voluntleers, but Amethyst does as well, which causes a fight. Garnet says that Amethyst should do it because Amethyst and Steven are good friends and the fusion would be stable. So, later on, Amethyst asks Steven to come dance with her. So, they dance and Steven gets really excited because he loves dancing, so then Amethyst's Gem starts to glow, as well as Steven's. And... Well, you know, they fuse.

It's just my theory, it is what I think.