I'm way too ugly to be Kara, but I can help a little on this one.

This can be common if you're feeding frozen thawed. Ball pythons hunt by sight, smell, and heat. When you dangle the rat into the cage/feeding container, your snake will smell the rat first ... then see the rat (but their sight is only good for things that are moving) ... and then look for its heat imprint (kinda like infrared). If you're standing behind the rat (especially if it's frozen thawed) your heat imprint will be stronger than the rats. Your snake will strike in your direction (sensing the heat coming from your body) and miss the rat. Sometimes they'll pick up on the heat in your hand and arm.

If the rat is the same temp or warmer than your body temp your snake should hit it dead on everytime.

That said, sometimes they seem to miss just because they are so eager to eat that they almost get too excited to hit their target. But that's just a crazy theory of mine and I don't have any evidence to back it up.

Hope this helps.

-adam