In the episode, deep underground, humans Amy Pond (Karen Gillan) and Nasreen Chaudhry (Meera Syal) have a conference with the Silurians' leader Eldane (Stephen Moore) over sharing the Earth between the two species.

Chibnall was selected by executive producers Steven Moffat and Piers Wenger to write a two-part episode about the return of the Silurians.

Meanwhile, Restac has killed Malohkeh for his betrayal and awakened other members of the warrior caste, intending to stage a coup against Eldane.

Writer Chris Chibnall was contracted by executive producers Steven Moffat and Piers Wenger to write a two-part Doctor Who episode about Silurians and a drill.

[1] Chibnall wanted it to be a "story about people making mistakes under massive pressure" and the accidental conflict that came out of protecting a family; as such, he always intended for Alaya to die.

[1] Moffat's plan "from the outset", to tie the episode into the overarching story arc of the series, was that Rory not just die but be erased from history in the crack in the universe.

[3] Moffat would later bring Rory back in "The Pandorica Opens", though the episode reveals his consciousness was placed in a Roman centurion Auton as part of a trap for the Doctor to save the universe from the cracks.

[3] "The Hungry Earth" and "Cold Blood" made up the fourth production block of the series and were filmed in late October and November 2009 in the Upper Boat Studios and Llanwynno, Wales.

[2] "Cold Blood" utilised many different locations and unusual sets to portray the Silurian city, as the production team did not want simply a "cave feel".

Set designers were able to rearrange the plants, though they had to be careful not to show the window leading to the car park or other modern amenities.

[10] "Cold Blood" was released in Region 2 on DVD and Blu-ray on 2 August 2010 with the episodes "Amy's Choice" and "The Hungry Earth".

While he considered it predictable, he said that it "still offered plenty in the way of entertainment with its brisk pace, beautifully-realised underground world and a convincing cast of rounded characters".

[17] Ian Berriman of SFX magazine gave "Cold Blood" four and a half out of five stars, positively comparing the emotional ending to episodes from the Russell T Davies era.