Chuck Berry's "School Days"

A couple weeks ago, Chuck Berry's "School Days" was in my head when I woke up.  Actually, it was just a single line:  "Drop the coin right into the slot."  And I noticed something about it:  both times it occurs in the song, the melody of the line descends, so it's something of a musical representation of the lyric itself:  the coin dropping into the slot.  I'm pretty sure the phrase is G' D Bb G (omitting repeated notes), so it outlines a G minor chord.