We know that cats walk very quietly, almost undetectably, especially when they are prowling towards their prey or in our cases, their toy or our legs.
Did you know that cats are the most inefficient walkers out of many different animals including dogs, horses, penguins or even humans? They use every single muscle in their legs very hard when they stealthily creep along, recovering little of the potential energy as their leg rebounds for another stride. This of course allows them to be extra sneaky and quiet to sneak up on their prey, but uses relatively more energy than we would for the same movement.
The below link will show you a study done by Duke University on the subject of Cat's Stride.