The official BBC Doctor Who website uploaded another special behind the scenes video diary of David Tennant's filming for the Doctor Who specials. In the 4th edition of the Tennant Tapes David Tennant records moments from filming Planet of the Dead, and you can watch the video below;

You can see a small glimpse of a Tritovore walking behind the Doctor and Christina at about 30 seconds in through the video. You can see all the previous editions of The Tennant Tapes here. Planet of the Dead will air this Easter on BBC One.