The most important clue to an unseen monitor's whereabouts is the track it leaves behind, such as this one from a perentie. Only expert trackers like Dr. Pianka can reliably "read" a monitor's movements in the desert sand and anticipate the animal's next move. But following tracks can be frustrating. One minute you clearly see the footprints, and the next, around the next bush, they vanish on hard, shrubby ground. Or desert winds just wipe them from the sand.