Children's percussion instrument native to the Whos of Whoville, from the 1966 Dr. Seuss animated television special How the Grinch Stole Christmas!
A tire-sized hoop with bells attached at four points on the interior circumference, it is played by standing inside and walking forward. Based on its size, you have to be very short to play it. It's unclear if the second person with a hand-held hi-hat is an integral part of the Trum-Tooker, or just a child-crippling accident waiting to happen.
The instrument is not in the original 1957 book.