Sometimes I see bubbly blobs of goo outside where I'm really sure no one spewed a spit. Here's one of them. It's a small glob of frothy foam dripping from a plant, and I generally see several of them if I find one.

I finally plucked a plant and used the stem to investigate. Inside the spit, I found a spittlebug:

I passed another spittlebug, and couldn't resist grabbing a photo of the bubbles it leaves in the lawn. This one was in the shade, so the bubbles were bigger. (Or perhaps there was a bigger bug in the froth, I didn't poke at this one.)

Here's a closer look at those white bubbles: