The tympanic membrane was a part of anatomy connected to hearing. Lizards' tympanic membranes were close to the skin which meant they could hear things incredibly loudly. The Ju'wes and Re'nar, which were anatomically similar, also possessed this feature. Mac'atyde could be driven off by a piercing sound from the sonic screwdriver or metal banging against pipes but was somehow unaffected by a Victorian firearm fired at close range. (COMIC: Ripper's Curse)