 Parry ( 1975 ) described how this species has a wider range of eye movement than other snakes . Along a horizontal plane , eye movement can be maintained even if the head is rotated up or down to an angle of up to 45 ° . If the head is rotated 360 ° , one eye will tilt up and the other down , depending on the direction of rotation . Also , if one eye looks forward , the other looks back , as if both are connected to a fixed position on an axis between them . In general , the eyes often flick back and forth in a rapid and <unk> manner . When asleep , there is no eye movement and the pupils are strongly contracted . The pupils <unk> suddenly and eye movement resumes when the animal wakes up . 
