Perhaps an example will do. Suppose "Perp" is sitting on top of a highway overpass. He has tested dropping bricks from there and knows how they will act. As a car approaches he watches closely and drops a brick with actual knowledge that it will hit the car. This meets the actual knowledge standard.

Let's change the facts. Perp sits there with his back to the highway, casually tossing bricks over his shoulder. He does not have actual knowledge than any brick will hit a car. However Perp knows there is a very real chance a brick will hit a car and he acts with callous disregard for that risk. This meets the reckless standard.