They won't do this if someone is near, so the photos are blurry. I was tiptoeing close and zooming in:
He caught me!
It's difficult to see from this angle, but the squirrel's entire underbelly is smashed up against the wood, his limbs bent out to the side. From above he looks like a chicken butterflied for the grill.
Likewise, this blue jay's underbelly is smashed up against the mulch, wings splayed, beak open:
They hold these positions, keeping absolutely still, for several minutes, choosing only dry, unvegetated surfaces. I'll think I have a dead animal on my hands and as I creep close they suddenly take off!