  We are developing a project aimed at studying the physical properties, origin
and evolution of low-ionization structures in planetary nebulae. Within this
project we have identified a number of pairs of highly collimated
low-ionization jet-like features (Goncalves et al. 2001). In spite of being
very similar to real jets, they have the intriguing property of possessing
expansion velocities which are very low, or at least not significantly
different from, that of the shells in which they are embedded. In this
contribution we discuss our data on these fake jets (Corradi et al. 1997, 1999)
and compare them with existing theoretical models for the formation of
collimated structures in PNe. These enigmatic jet-like systems are not easily
accounted for within the theoretical scenarios that deal with collimated
features in PNe.
