Have you ever inherited code, made a simple change, had it completely fail to work how you thought it would, and spent hours hunting down a subtle bug in your change? It might not be entirely your own fault! The previous developer may have laid one or more booby-traps for you to step into. (Then again, that may have been "past you"!) This talk will help you spot many kinds of such traps before you trigger them, and avoid laying them yourself.