It is described as an indiscernable white object, like a big, slender paper strip, or a white, loose textile sheet, that shimmers and wiggles as if moved by a strong gust of wind, even on windless days.
It is described as a white streak, like a big, slender paper mannequin, or like a white, loose textile streak. It's wiggling the whole time, as if moved by a strong gust of wind, even on windless days.