Actually, as Reviewer 1 noted, we use a viscosity that is 1000 times greater than that of water (following Wolgemuth et al. 2005), for the very reasons the reviewer mentioned.
In the force balance, the drag coeffcient is assumed to be the viscosity of water. Since the cells glide over a surface and next to other cells, it would seem that cell–cell friction and cell–surface friction might be at least as important as hydrodynamic drag. What about the viscosity of the material used in the “slime jet”?