To elaborate on Tommy's answer, pressing Z activates your amulet, anything within a reasonable range (looks like something in the order of 10 to 15 meters from Geralt) carries a sustained orange glow for a minute or two if it can either be 1). activated (doors, traps, etc) or 2). is a lootable container. (including plants with ingredients and bodies) This can, on a few occasions, get annoying as there are a few containers that you just can't get in the right position to loot. In the town before going down into the sewer there are at least 2 small cabinets and a bookshelf that contain something but the furniture arrangement makes it impossible to get within range. However on the plus side you will find that there are also occasions where bodies have disappeared before you have has the chance to loot them, pressing Z will highlight the positions where the small remaining loot sacks are, quite often these can be obscured by undergrowth and other statics, but using this method you can find them.