[Doctor Who is copyright the BBC: respectfully, NO INFRINGEMENT INTENDED]; this is an expositional [additional] scene, literally between "The Eleventh Hour" and "The Beast Below" (a little awkward with Amy's line delivery in spots), but a nice reminder of how the Chameleon Circuit works, and why the TARDIS is a Police Box (as well as why Amy is floating outside the TARDIS at the start of "The Beast Below").