"杮" (kokera) indicates a piece of wood or wood shavings as in "kokera" in "kokera-otoshi" (literally, dropping kokera and actually, meaning the opening of a new theater: this term originates in that pieces of unnecessary wood are dropped after the building work completed).
「杮（こけら）」は「こけらおとし」の「こけら」同様、木片・木屑の意味。