Intuitively, I believe that you can't push out more than one adjacent "feeler" per turn, because otherwise the cells behind it would be so dense they'd kill the

Intuitively, I believe that you can't push out more than one adjacent "feeler" per turn, because otherwise the cells behind it would be so dense they'd kill themselves in the next round. So you simply can't get enough density to move more than one step in any given direction per two cycles.