The TARDIS on the cloud was achieved through a mix of fog on the studio floor and post @-@ production special effects . Director Saul Metzstein explained that it was difficult to achieve the desired look for the snowmen ; the first ones he likened to Zippy from Rainbow which was too " cute " of an appearance , and so the effects team created more menacing CGI faces . Clara 's introduction to the TARDIS introduced two novel effects for the show . The first was a single @-@ shot camera tracking from a few feet away from the TARDIS to its interior , with the implication of the TARDIS 's trans @-@ dimensional nature shown to the audience . In the following shot , the camera does a complete circle of the TARDIS console , an effect not seen since the early days of the show . Metzstein wanted to include this shot to further emphasize the " bigger on the inside than the outside " nature of the time machine .