A thick-skinned monster is a monster that will only be dealt one hit point damage when attacked by a bullwhip. Thick-skinned monsters have the flag M1_THICK_HIDE in the source code. The following monsters are thick-skinned: * Gargoyles and winged gargoyles * All mimics * Mumaks, titanotheres, baluchitheriums, and mastodons * All dragons (including the Chromatic Dragon and Ixoth) * Earth elementals * All nagas * Xorns * Skeletons * Wood, clay, stone, glass, gold, and iron golems * Horned devils and barbed devils * Sharks * Crocodiles and salamanders