Watched line go back and forth between faint and BFN.

Shrimpy
Has anyone ever watched a faint line go in and out (several times) before their eyes? Or is this a rookie question? After 4-5 minutes, I would say it finally stabilized as faint (camera battery died at same time (of course)). 10 days dpo, so will test again in a couple days, but still super curious. Test: first resp. early res./FRER. Thanks!