When photographing subjects like wildlife or children where expressions and body language can change in a heartbeat, don’t take your eye away from the viewfinder or you risk losing a great shot.
A case in point is this Siberian tiger my photo tour group and I were photographing in China. I was able to catch this aggressive display because instead of lowering my camera and watching him directly, waiting for a great shot, I kept my eyes glued to the viewfinder with my finger on the shutter. In this way, I was able to capture a very dramatic image. Moments like this are very fleeting, and if you aren't ready to shoot instantly, the moment will be lost.
I particularly like this picture because it looks like the illustrations I've seen of the extinct sabre tooth cats. Siberian tigers don't have four-inch long fangs like the ancient cats did, but this picture could very well depict what the sabre tooths looked like when they hunted and fought over food.