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\item What happens if an interior piece approaches the pore?  \item In \citet{http://adsabs.harvard.edu/abs/2013PhRvE..87d2723R} page 5, it is claimed that motion will be a superposition of longitudinal and transverse. Is this true -- won't one of them be unstable (in the case where work done in dragging is less than $T$, say)?  \item Same paper, page -- dimensional analysis. Try to do a better job than scaling argument: what are the coefficients? The fact that in the other paper they are off by some distance might be to do with this kind of thing.  \end{enumerate}