Antique Book Shaped Slide Whistle with Surprise Heart and Scale, Working BeautifullyTruly a wonderful thing. Shaped like a book, at first I thought this was an old spruce gum box always something to get excited about! but then I saw the hole (called a fipple, I've learned) at the base of spine side, and the carved knob at the top, and I realized it might be an extra beautiful slide whistle. Once I had it out of the case at the shop where I spotted it, I discovered to my great delight that the slide was carved out with a big heart