In "The Name of the Doctor" the Great Intelligence found the Doctor's grave on Trenzalore. The TARDIS contained the Doctor's entire timeline, represented as bright lines. The Great Intelligence was able to enter the Doctor's timeline, fracturing himself into various aspects that each appeared at different points in the Doctor's timeline. In order to stop the Great Intelligence, Clara also entered the Doctor;s timeline, resulting in various Claras all across the Doctor's timeline. The Claras from "Asylum of the Daleks" and "The Snowmen" are two of those splinters of Clara.