In this generally delightful warm fuzzy song with its subtly soft eroticisms compatible with the nice-Nellyism of singer Anne Murray, the word "good" is misued as an adverb, apparently in order to make a rhyme. "Good" is, properly used, an adjective. The correct adverb would be "well". It would seem hard to correct the grammar and still make a rhyme. I don't know how common willow woods, as opposed to other types of habitats, are in Anne's native Nova Scotia. I have greater experience in the southeren Appalachian mountains, where various shrubs of the heath family, including rhododendrons, azaleas, mountain laurel, blueberries, and dog-hobble, form dense thickets, very hard to penetrate. Although the heath family is not at all closely related to the mainly old world laurel family, most if not all of those members of the former have been collectively dubbed "laurels" because of a superficial resemblance. Early settlers, wanting to travel through the Appalachian area, dubbed those dense thickets "laurel hells" because of the formidable barrier that they presented to passage through, and the name somewhat sticks to this day. That gave me an idea how both rhyme and grammar might be preserved, had the song's setting been the southern Appalachians, at least. It could have been "There's a wren in a laurel hell. / Flies so high and sings so well." But that has qualities that could detract from the song's romance. Incidentally, I'm not sure of the aptness in any event of referring to a wren as flying so high. Perhaps wrens are entirely capable of flying high. But all kinds of wrens that I have any knowledge of have habits that keep them fairly close to the ground much of the time. They like to frequent undergrowth and tangles of fallen wood.