I recently heard "We Can Work It Out," and I realized that there's a time signature change in the bridge. It's mostly 4/4, but it changes to 3/4 for "fighting, my friend" and again at "ask you once again." At first I just thought, "Oh, there's an-other Beatles song that mixes time signatures." I learned years ago that "Lucy in the Sky with Diamonds" does this (the verses are in 3/4 and the choruses in 4/4), and I recently discovered that the end of "Mean Mr. Mustard" changes time signatures too.
I got thinking about this later though, and I realized that this change in time signature is significant with regard to the lyrics. The first couplet of the bridge is "Life is very short, and there's no time / For fussing and fighting, my friend." In that change from 4/4 to 3/4, there's one fewer beat in a measure, so there's a musical representation of the brevity that's mentioned in the previous line.
