They just love skimming the surface vacuuming up the white fuzz. Its not uncommon to witness pods of carp just wallowing and sucking up cottonwood, their funny toothless mouths wide open, hoovering up the white fuzz. Of course this is the time also to start throwing Cottonwood top water flies if you dare. I like to tie up a foam parachute with white hackle for my Cottonwood flies. The fly floats high and I can see the white parachute better than just an all white hackle. You can see an image of that fly here. I have to honest and say, its freaking hard to catch them on a Cottonwood dry fly and when I have no luck doing that, I switch to my backup plan. A white Zimmerman Backstabber.
This guy turned and followed the fly to the bottom of the pond before sucking in the fly. That's the thing with this type of fly. The initial splash will often times get their attention and the action of the marabou really makes them want to bite. I have seen carp take the Backstabber as it falls through the water column.
After a bit your fly kinda of gets beat up. But even then the fly continues to produce.
I did run into this guy while out hunting carp. A nice 5 foot or so Bull snake just hunting along the shore with me.