The youngest protostars are obscured from direct view by a high column of
molecular gas. Nevertheless, their presence is betrayed through spectacular
infrared outflows.
Infrared spectroscopy should reveal many details of the underlying physics.
Near-infrared spectroscopic observations and analyses of the high-mass outflows OMC-1, Cepheus A and DR21 are presented here. The implications for supersonic molecular dynamics are derived. In particular, shock physics and shock structure are discussed.