the_content filter, but for RSS?

I want to write a plugin that does something special to post body content, but only in RSS feeds. I don’t want my special munging to show up in HTML at all.

I see a filter called “the_content”, but there isn’t a “_rss” version of it the way there is for “the_title” and “the_excerpt”.

Is there something I can test for to see if the_content got called from an RSSish context? Or is there a different filter hook I should use for this?