HST images taken over a time span of 11 years show that the tips of its bright optical fingers have proper motions exceeding 1". At the presumed distance of 0.9 kpc, the proper motions are equivalent to projected speeds of over 400 km s^-1. However, optical STIS spectra (Riera et al 2011) and our narrow-band images from the tips of the fingers suggest that the radiation arises at a shock speed Vs 80 km s^-1. A forward shock at Vs >150 km s^-1 is far too fast to be observable except, perhaps, in x-rays. So the observed emission lines must arise from a secondary shock driven into the clump or jet (the latter case seems highly unlikely). We will present highlights of hydro models that compare the expected differences of excitation and the shock structures between clumps and jets.