Winning over the minds of followers and converting non-believers are the fastest way for a lesser deity to grow in power and influence. Entrancing a random bat and consuming his sanity (she IS a chaos deity, after all) like a refreshing milkshake is far less efficient... but there's something to be said for style.

In a way, this is win-win. Eris gets her snack, a tiny power boost, and a new puppet, and the bat... well, the rest of his life will be worry-free, content to over Eris's whims.

The SAN and Divine status bars are definitely inspired by  diorexity's cool and creative status bar vore images.