We’ve got to grow it on her brow

My son, who has his bedroom adjacent to the kitchen where the radio plays, stomped out of his room very confused this morning.

“What kind of song is this? Why do they keep singing ‘we’ve got to grow it on her brow?’ I don’t get it! Grow what?!”

“Um, the lyrics are actually ‘we’ve got a groovy kind of love’ but I think I like your version better.”