The only way to be sure you weren't decapitating your subjects was to become accustomed to your particular camera through practice, practice, practice. Today, many cameras still use the same method of focusing, so you still need to be careful. There's no easy way to overcome the risk, although modern viewfinders are marked to help you. Be sure to pay attention to the background. Here the background not only is distracting but makes it difficult to see the subject.
Pros use a telephoto lens with a wide open aperture to throw the background out of focus.
Although many viewers may get a laugh out of the illusion, Uncle Bob may not appreciate the humor. Also, I personally have collected several photos of my feet and the open sky by having my finger on the trigger before I was ready to shoot. My favorite goof-up story involves a great blue heron. Herons are much more difficult to approach than an egret is. One day, at a wildlife refuge, I had my tripod set up with a 300mm lens.