Justin Bieber has made something of a habit out of making surprise public appearances lately -- as these wedding guests can attest -- and he continued his streak Tuesday night at the Staples Center in Los Angeles.

What was so unexpected about Bieber taking the stage in L.A.? Only the fact that Taylor Swift was already there, wowing a crowd of several thousand fans -- who really went into a frenzy when they saw her special guest.

Bieber and Swift then broke into a duet performance of his big hit 'Baby,' trading verses and yielding the mic to the crowd during the chorus. Apparently feeling especially frisky, Bieber even threw in Ludacris' verse from the remix version.

Sure, it was a much tamer surprise than Swift's recent wardrobe malfunction, but listen to those explosive tween screams -- could this be the cause of yesterday's earthquake?

Check it out below:

[via PopCrush]