When Nahad looked under the door all he was black.  The shadows had covered everything and they were between the bottom of the door and the rest of the room.  When he tried to use his other sense nothing could be felt.  The shadows he had created separated what was inside of them and outside of them perfectly.  Nothing from the outside could get in and nothing on the inside could get out.  It let the user make as much noise inside without alerting anyone outside.  This technique is what had earned him great respect as an assassin in his village, at the age of 9.