Facebook must be a little envious of Twitter's ability to seize on trends -- it just started experimenting with Trending Topics, a Timeline card that shows the hottest subjects on the social network. Users can tap a trend to see both public comments and posts, whether or not the contributors are friends. The service is only being tested with a small number of those using Facebook's mobile website right now. If you're too impatient for that, the company has a consolation prize:
