Having seen ivy rope-throttle full grown trees, it isn’t hard to imagine a holly smothered in it.  I like the crow’s ‘aa-aa’ commentary before going back to its meditations.

‘A crow awoke in an ivy-thick holly, muttered aa-aa, and laid its beak among its neck-feathers once more.’

Source: Henry Williamson, Tarka the Otter: His joyful water-life and death in the two rivers, illus. C.F. Tunnicliffe (Harmondsworth: Puffin Books, 1976 (1927)), p. 57