A couple days ago, I was thinking about "I'm So Young" and realized that in various points in the lead and backing vocals, "so young" is sung with melismas (I'm not going to go through and figure out specific pitches for every instance). Musically, this provides emphasis and gives a sense of degree.
I also quickly referenced the version by the Ronettes, which predates the Beach Boys' version. The lead vocals have this feature, but I don't think the backing vocals do.