When Drakus is listening to the device placed on Londo in down below. He is listening to the location of Nideera with N'Grath. At times when N'Grath moves around you can see gaps from the head showing that it is hollow and some of the hoses for the hydraulics for the puppet to move the head. You can also see there is a gap between where the eyes are and the rest of the skull as the light shines in from the background.