A bombe run involved a cryptanalyst first obtaining a "crib" — a section of plaintext that was thought to correspond to the ciphertext. Finding cribs was not at all straightforward; it required considerable familiarity with German military jargon and the communication habits of the operators. However, the codebreakers were aided by the fact that the Enigma would never encrypt a letter to itself. This helped in testing a possible crib against the ciphertext, as it could rule out a number of cribs and positions, where the same letter occurred in the same position in both the plaintext and the ciphertext. This was termed a "crash" at Bletchley Park.