One of my old classmates' area of research is applying electric stimuli to various types of cells. Apparently the right amount at the right time can briefly allow foreign material to pass through the cell wall unimpeded. The complexity of a single cell is insane, that of a complex organism is way beyond insane.
I think you meant cell membrane rather than cell wall?
(There is a contrarian theory that says that the cell membrane does not exist at all, look up Gilbert Ling. So it's no surprise that things can move in and out of the cell under certain conditions.)
