  Many low-mass stars in the Orion nebula are associated with very compact (~=
1 arcsec) emission knots, known variously as proplyds, PIGs or LV knots. Some
of these knots are teardrop-shaped, with ``tails'' pointing away from the
massive star Theta 1 Ori C, which is the principal exciting star of the nebula.
We discuss models of such knots, which invoke the interaction of the fast
stellar wind from Theta 1 Ori C with a transonic photoevaporated flow from the
surface of an accretion disk around a young low-mass star. We review previous
analytic work and compare the results of the model with the observed
brightnesses, morphologies and emission line profiles of the knots, as well as
presenting new results from numerical hydrodynamical simulations.
