Onomatopoeia. This is the literary convention of creating and using words that mimic sounds, such as “squeak”, “hiss”, and “Ka-Boom!” Rivera’s noteworthy contribution is the creation—or use of—everyday words as sound effects. While “SLAM” is a standard sound effect label, “WALK” is one of Rivera’s own, along with earlier instances, such as “STOP!” (for a car coming to a quick stop) and “CLENCH!” (for a fist clenching), as used in earlier stories.
Now, “WALK” certainly seems to suggest a deliberately aggressive walk, resulting in a distinct sound of feet slamming the floor. Rusty’s posture suggests such an interpretation. It is more interesting than the traditional “STOMP! STOMP!” But is it more than this? It could be a symbol for a sound that we must complete in our head; we each may have our own impression of that sound. Or maybe it’s a bit of satire. Your thoughts?
Finally, it is interesting that Rivera uses a similar visual “syntax” for both sound effects. The bordered orange “SLAM” effect actually appears like a fitted overlay to Rusty’s door, implying that the sound fully incased it. An inventive solution.