When photographing wildlife it is considered a must to get the creature's eyes in focus, unless of course you are photographing a flock of birds where that would be impractical or almost impossible. When using a telephoto lens the "depth of field", or area in the photo that is in relative focus diminishes as the focal length of the lens increases. A 500mm lens, as was used for this photo, can have a relative depth of field that amounts to only a couple of inches! When "shooting" more than one subject you want their eyes to be in the same focal plane so they will all be in focus in the photo. The scene in this photo started out as two fox kits watching me watch them. After taking a few shots I saw the third kit emerge from the den entrance directly behind them. As it squeezed in between it's siblings, I shot a burst of photos as it jockeyed for position. Out of about 12 photos taken, four photos had all six eyes in focus. The "eyes have it"!