In this paper, we report on the formation and rupture of Ag nanofilament on planar Ag/TiO2/Pt cells using visual observation. During the forming process, the filament tends to stay very thin. Specifically, it is so thin that it breaks up into a chain of nanospheres (according to Rayleigh instability) right after the formation has been completed. Similar mechanical breakup may also impact vertically stacked cells, causing reliability concerns.