I just listened on Spotify to a recording from the album "Vanguard Visionaries: Country Joe & the Fish" (2007), which I think might be the original recording that was released as a single back in 1967. Here is a detail that I haven't seen documented, and which may have escaped the notice of most listeners: During the choruses, one of the band members is chanting in the background:

Chorus 1: "…doo-wacka-doo-wacka-doo-wacka-doo..." etc.

Chorus 2: "...sock it to me, sock it to me, sock it to me..." etc.

Chorus 3: "...psychedelic, psychedelic, psychedelic..." etc.

Chorus 4: "…doo-wacka-doo-wacka-doo-wacka-doo..." etc.