Abstract
This paper first reviews the literature of entrainment of molecular material into HH jets. The available models can, in principle, reproduce the H[2] emission of a number of HH objects. However, there are some HH jets with aligned knots which show basically identical structures in the H[2] and atomic/ionic line emission. For these objects, we suggest a possible interpretation in terms of the ablation of molecular gas from dense clumps which are immersed within the jet beam.
