squirrel cage

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A circular cage for a squirrel or other small animal, which rotates vertically as the animal runs at the bottom.
• noun figuratively, by extension A tedious, repetitive, unfulfilling activity or situation, especially one in which no progress is achieved.
• noun engineering Any other device, such as a fan or rotor, that resembles a squirrel cage in form.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun cage with a cylindrical framework that rotates as a small animal runs inside it