Well I can see it literally foaming up before my eyes and I don't see any bugs in the foam. I thought maybe the plant roots were releasing oxygen as they were filling with water or maybe the plant produces saponin and the rain drops/air/saponin combination is making foam. They're selenicereus grandiflorus roots.

That's interesting, can't tell you why. Still interesting.

Science is too cool. Wonder why it is happening. Be neat to know.

That's odd, but fascinating.