Both Cassandra and the robotic spiders — other than an inactive one — are completely CGI creatures. According to Russell T Davies, Cassandra was worked on for "many many months" and costed a "fortune". The Moxx of Balhoon was originally going to be animated, but this changed to a "glove puppet" and then a full rubber suit when it was desired he be "chunkier". Actor Jimmy Vee had done similar parts before, although the actor said it was hard filming in the costume, which took three hours to put on. Jabe was originally more tree bark-like in the face, but it was decided that she be a Silver Birch instead.