Cretins have physical deformities as well as impaired metabolism and low body temperature. Poor hearing is marked and permanent (often manifest as deaf mutism), and mental retardation is often at the level of idiocy. Cretins are slow moving, sleepy, and halting of speech; the acquisition of knowledge and skills is a difficult and time-consuming process. The height of cretins is well below average (146.7 cm for males and 140 cm for females).