The Self-Inflating Hedgehog

This small creature is an evolutionary response to the huge number of very heavy steam engines in the City. Hedgehogs with flexible joints and compressible organs survived more than those without, and symbiosis with a tick that acted as a one way outlet valve completed the process. Being run over creates a loud, interesting noise, and it has become an urchin pastime finding these shy creatures and placing them under wheels, much to the dismay of the Ladies Civic Improvement Society.