The Gossip Girl star took to the stage this Halloween...

...and joined band Weezer onstage at the Hammerstein Ballroom in NYC on their song (If You're Wondering if I Want You To) I Want You To!

Check her out here:

We noticed two strange things about this video:

1) The Teletubby heads (Tinky Wink and Po if we're not mistaken) bopping about in front of the person filming around 1:30!

2) Leighton's outfit - we really hope those multi-coloured trousers and black top with holes in the arms were part of a Halloween costume - points to anyone who can tell us who she was meant to be?!

Click next to see what else Leighton's been up to!