Banksy is an "art terrorist" who pulls cultural pranks by secreting his work into museums and performing stealth installations. The pieces don't get noticed for weeks at a time and then everyone has a big laugh. Love the play on the credibility that museums give art and artists.
Back in the '80s Jeffrey Vallance was an instructor at Otis-Parsons in LA, who I had met briefly, and he did a similar thing where he painted electrical outlet covers and installed them at LACMA. He then sent out invitations to his "opening" at the museum. It's all documented in that RE/Search book Pranks!.
Anyway, Banksy just put another piece in the British Museum, a fake artifact with a man pushing a shopping cart that is characterized as "early man venturing towards the out-of-town hunting grounds." I love it, the Beeb loves it, and the British Museum loves it. What's not to love?
Cave art hoax hits British Museum
Props to Carbongeek for finding it first.