The Doctor first reveals sonic screwdriver's weakness with wood in Silence in the Library (2008). In the same story he later mentions some hair dryers could also pose a problem for it.
For the scene in which Amy is dragged underneath the ground, Karen Gillan stood on boxes and lowered herself into a stone compartment. Two pieces of rubber were at the opening of the compartment which expanded as she lowered herself down. A layer of soil was spread across the rubber; Gillan's ears were taped over to make sure the soil did not enter her ears. Gillan, initially scared at performing the stunt, put some of her fear and claustrophobia into the scene as she expected Amy felt the same way.
Chris Chibnall wrote for the redesigned Silurians to be beautiful and it was intended for the redesign to capture the actors' features and allow them to give stronger performances and differentiate themselves. Chibnall believed that it complemented the theme in the two-parter about how the humans and Silurians were alike and different.
In the early stages of production, the new Silurians' masks were intended to be quite similar to the originals, only with green scales.
The completed episode had a running time of sixty minutes, requiring over fifteen minutes of footage to be removed to fit its broadcast slot. Much was originally made of the fact that the Discovery Drilling Project was under pressure from its financial backers to reach greater depths more quickly.