We discuss here the nature of a rich zoo of knots, filaments, jets and jet-like systems, located--in terms of morphology and kinematics--either inside or outside the main nebular bodies of planetary nebulae (PNe). These features are low-ionization structures (LISs) especially prominent in [N II] and other low-ionization line emission, which are usually smaller than the main morphological components of the PNe (spherical and elliptical shells, bipolar lobes, and haloes). We have recently shown that LISs are equally spread amongst all morphological classes of PNe (Gonçalves, Corradi, & Mampaso 2001).