  Knots (emission features in jets of active galactic nuclei) often show
non-ballistic dynamics and variable emission/polarization properties. We model
these features as emission pattern propagating in a jet that carries helical
magnetic field and is launched along a changing direction. The model can
reproduce a wide range of phenomena observed in the motion of knots:
non-ballistic motion (both smooth and occasional sudden change of direction,
and/or oscillatory behavior), variable brightness, confinement of knots' motion
within an overlaying envelope. The model also reproduces smooth large
polarization angle swings, and at the same time allows for the seemingly random
behavior of synchrotron fluxes, polarization fraction and occasional $\pi/2$
polarization jumps.
