As Walt says here, "Chemistry is the study of... Transformation!" It's a metaphor for the series, and it was an expert bit of foreshadowing from the show's writers. Little did we know when this episode premiered that we'd see Walt transform from "Mr. Chips into Scarface," as Vince Gilligan has so famously put it. The scene's memorability was probably enhanced by the endless Junip-fueled teaser trailers that AMC ran leading up to the Series Finale. This scene is interesting to watch with 20/20 hindsight, because it provides significant insight into Walt's character. Here we have a man who's inspired by the science of chemistry at a truly deep level, but who hates teaching it to the little b**tards in his class. Considering Walt is one of the most brilliant and ruthless criminal masterminds in television history, it's a wonder that Chad escaped with his life.