I had to collect myself for a minute but all right, here's the deal: The song is the first song on Led Zeppelin II, setting the standard for any rock song to come after. It was based on a song recorded by Small Faces a few years before titled You Need Loving, itself a cover of a Muddy Waters song written by famed bluesman Willie Dixon. The vocal delivery is modeled after Steve Marriott of the Small Faces rendition of the tune, but the song was changed and morphed into something raw, new, and dangerous. The middle freakout section has become infamous, even more so when American radio tried to cut the track down to make it more radio friendly, but Led Zeppelin refused to release a shortened version of the song as a single; FM radio made their own, catapulting the song into history. The section included sexually charged wails by Robert Plant, percussion by Bonzo, and the strangled, otherworldly sounds of a device called a Theremin. Adjusting the controls and waving your hand around the antennae of it caused the different tones of the scary sounding machine and Jimmy Page used it to devastating effect in the studio and during live performances.
Fun personal fact: I used to make my mom play this song on her 8-track player and rock out to it, then literally freak out during the freak out part. As a 3 year old it made me think of a tornado or a freak storm, tearing through a valley and ripping everything apart. Good times!
And here's the version of You Need Loving by Small Faces. Steve's vocals are still blowing my mind.