The speed of the curve
is the length of the first derivative. For a non-zero number of rotations
within the Frenet frame, the amount of rotation is proportional to
the speed. It can be observed from the difference between the twisting
to the same knot with zero rotations. The models in the first and
the last rows wind once around the meridian. If for these models we
have R = 2r, then the motion of the Frenet frame has a discontinuity
at cost = 0 and sint = 1. This is the reason for the
rapid twisting in the neighborhood of the point where the curve passes
through the narrow neck of the torus.