Dissapearing cloud

Hi, this is my first thread - i usually lurk around watching what is going on - just i wondered if anyone knows much about clouds - i was outside a min ago (it aint windy) and i saw these strange swirly thin lines in the sky (was a blue clear sky) and then i turned around for about 5 seconds then turned back and they were gone and i went to look out of the front and they werent in the sky there either - i thought at first they were airplane smoke but then i saw it was way to thin as that expands - it was like three peices of string - i would put it down to clouds but i dont know how they can dissapear in 5 seconds when they were right over me.