 It has been hinted that he is actually agoraphobic and enjoys dark, enclosed spaces.  Though he only performs roughly four hours of duty per day as Warden of Impel Down, he still takes his role quite seriously and does not tolerate the prisoners' bad behavior. As he has permission to execute any one of them he sees fit, he shows no hesitation to drench them in his Hydra's lethal poison, as seen with what happened on Level 6 when insulted by prisoners.  