Unlike Facebook, where friends mutually agree to let one another into their online lives, Twitter lets people share updates and links with anyone who cares to read them.

That has turned Twitter into a tool for people to peer into the collective mind and see what people are talking about in real time. It is also a tool for businesses to reach customers and monitor what their customers are saying about them.

Facebook seems to be very interested in those features. Since last fall, when Facebook tried and failed to acquire Twitter, it has been slowly introducing features that mimic Twitter.

Last week, Facebook added two new, Twitter-like features. Users can now