"DIS-SEM-IN-ATE! DIS-SEM-IN-ATE!" The cow advanced a step further towards the two time-travelers, its eyes glowing a menacing red. The plunger-udder waggled menacingly, and Rose backed away a step. There was an unpleasant scent in the air, and she began to cough. Her chest felt like it was on fire, and her eyes were watering.
The Doctor seemed unaffected by the Dalek cow's new attack. "Methane. They've re-modeled themselves after a species that produces it in vast amounts, and now they're planning to replace Earth's atmosphere. Wipe out the entire human race, all at once." There was a touch of admiration in the Time Lord's voice despite the grim words. He hated his arch-foes, but had to grudgingly respect their dedication and ingenuity.
He turned back to Rose, where she had all but collapsed beside him. "Right, then. Into the TARDIS with you." He reached down to get an arm under her, hefting her back to her feet and guiding her towards the nearby police box. As he reached into his pocket for the key, a manic grin spread across his face. "We've got a planet to save!"