 In the serial "Destiny of the Daleks",<ref name="destiny"></ref> Romana was able to voluntarily stop both of her hearts beating, to fool the Daleks into believing that she was dead.The Doctor also shows a greater tolerance to cold compared to humans in "The Seeds of Doom"<ref></ref> and "Planet of the Ood"<ref name="Planet of the Ood"></ref> and even Romana in "The Ribos Operation",<ref name="ribos operation"></ref> and in "42",<ref></ref> the Tenth Doctor states he is able to survive at absolute zero for a short period of time.In "World War Three",<ref></ref> the Doctor is able to shake off an electrocution attempt which is fatal to a number of humans, and appears unaffected by the energy whip wielded by the Sycorax in "The Christmas Invasion".