Some years ago while we were walking in the woods, I heard quacking coming from a small pond a little way off the trail.  Mallards, I though, and brought my binoculars up to take a look.  I couldn’t find them, even though mallards are not known for cryptic coloring or a retiring manner.   A few days later, the same thing happened in a different spot — phantom mallards.  I was starting to get confused; I know my eyesight is not the best, but I can usually rely on my ears to tell me what’s going on around me, and my ears were leading me to invisible ducks.   Eventually my friend Andrew enlightened me.  Turns out there’s a creature called a wood frog…