What's under the leaf?

This morning the migraine had faded away and there was beautiful frost in the garden (we haven't had snow).
I sent out to explore with the macro lens.  It was only when I looked at one of the 'frosty dead leaf' images on the camera screen that I realised there was something curled up under the leaf. It looked like a pupa or a cocoon, but I didn't want to poke around and disturb it.  There was a second one very nearby, see extra.
Maybe it was some kind of growth on the underside of the leaf, and not a creature at all. We'll see, in the fullness of time. I've left it undisturbed.