We don't yet support GIFs when uploading images to Cake, but you can paste a URL to create an embedded GIF:
Hmmm...the preview shows a full link. Let's see what happens on publish.
Boo, gif embed fail.
Hmm. The trick with Giphy is to use their "Copy Link" feature to get a link directly to the GIF itself. If you link to Giphy's landing page for a GIF, then it'll be treated as a web page link rather than an image link (I think maybe that's what happened there?).
Btw, the editor really is WYSIWYG, so no need to publish to see what the embed will look like. 🙂
I always used "Copy image address" when embedding Giphy on Facebook, so that's what I did here, but it still borked. However, using the Copy Link feature does work as expected. And noted on the WYSIWYG.