  After their birth a significant fraction of all stars pass through the tidal
threshold (prah) of their cluster of origin into the classical tidal tails. The
asymmetry between the number of stars in the leading and trailing tails tests
gravitational theory. All five open clusters with tail data (Hyades, Praesepe,
Coma Berenices, COIN-Gaia 13, NGC 752) have visibly more stars within dcl = 50
pc of their centre in their leading than their trailing tail. Using the
Jerabkova-compact-convergent-point (CCP) method, the extended tails have been
mapped out for four nearby 600-2000 Myr old open clusters to dcl>50 pc. These
are on near-circular Galactocentric orbits, a formula for estimating the
orbital eccentricity of an open cluster being derived. Applying the Phantom of
Ramses code to this problem, in Newtonian gravitation the tails are
near-symmetrical. In Milgromian dynamics (MOND) the asymmetry reaches the
observed values for 50 < dcl/pc < 200, being maximal near peri-galacticon, and
can slightly invert near apo-galacticon, and the K\"upper epicyclic
overdensities are asymmetrically spaced. Clusters on circular orbits develop
orbital eccentricity due to the asymmetrical spill-out, therewith spinning up
opposite to their orbital angular momentum. This positive dynamical feedback
suggests Milgromian open clusters to demise rapidly as their orbital
eccentricity keeps increasing. Future work is necessary to better delineate the
tidal tails around open clusters of different ages and to develop a Milgromian
direct n-body code.
