When he was one year old, Clerc fell from a chair into a fire, suffering a severe burn and obtained a permanent scar on the right side of his cheek. Clerc's family believed his deafness and inability to smell were caused by this accident, but Clerc later wrote that he was not certain and might be born deaf and without the ability to smell. The facial scar provided later the basis for his name sign, performed with the manual alphabet for "U", stroked twice downward on the right cheek.