She made the sombre crowd cheerful by her erratic and glistening ray, even as a bird of bright plumage illuminates a whole tree of dusky foliage by darting to and fro, half seen and half concealed amid the twilight of the clustering leaves.
There are no more uses of "erratic" in the book.
Show samples from other sources
Bus service was erratic and seemed to go nowhere, but the Federal Government had forced a highway or two through the swamps, thus giving the citizens an opportunity for free egress.
Harper Lee -- Go Set a Watchman
He’d given her an inappropriate, clumsy, but very direct compliment that she knew she would never forget and that had already set her heart to a new and erratic pounding.