I was on a united airlines flight from lax to smf. i was continuously looking out the window to view the landscape below. when we came upon a flat cloud cover i was looking down upon. not able to the landscape i started observing the clouds. for as far as i could see it appeared to have such an even top surface. i thought there must be an altitude reason for that. then came up on a tall cone like blast that went up out of the flat surface. as if something came up out of the clouds at that spot and took some clouds with it for a ways. looked very odd. i then began to be more observant. we then came up on what looked like a circle like cloud. didnt seem normal either. i was staring at it when i saw this rod like cloudy thing appear out of nowhere. it started to get larger. it then started to move like a snake, it had motions on both side. i nudged the next to me, and said you have to see this. he said its looks like a rocket. then it stopped and moved like a snake. i felt sure that this thing had intelligent motions as if it was alive. lost sight by passing it by.