Some Midwesterners and many speakers in the Eastern States pronounce cot and caught as /kɑːt/ and /kɒːt/. (Pronunciation and spelling information from Handschuh and de Geigel, Improving Oral Communication (1985)) Speakers who pronounce both types of words with the vowel /ɑː/ might not hear a difference and might not know why Midwesterners misunderstand them.