Spring is here, spring is here, how do you think I know?

Phoebe's been singing a song lately about spring. It's interactive, so she sings:

"Spring is here, spring is here, how do you think I know? I saw..."

And you're expected to reply something to the effect of...

"...flowers blooming in the garden"...

And then she starts again... and again... and again...

Well, here's how *I* know it's spring!