There are a helix groove of half rev. (n = 1/2) on the big torus. The small torus makes 1 rev. around its axis during 2 rev. around the big torus axis. In other words, the small torus has two interdependent rotary motions.
It is case of Mobius strip (figure on the upper left corner), an ant must crawl two rev. to get the start point.