At approximately 6:55 AM on January 16, 2016, I was walking my dog. Our house is essentially directly below the flight path for planes landing at Honolulu International Airport and I always look at every plane just to see which airline it is. I saw a plane approaching from the west (I was also facing west) at an unknown altitude, looked up and saw that it was a Japan Airlines plane and kept walking. My dog stopped to sniff the grass and I turned around (now looking east) to look at the plane again. My attention immediately went to a seemingly normal nimbus-type of cloud that was at a higher altitude than the plane. As I looked at the cloud, I saw a perfectly straight line being traced/cut through the cloud as of something was flying through it but there was absolutely nothing there. I wasn’t sure what just happened so I just kept staring at the cloud and roughly 15-20 seconds later, the cloud had continued its normal movement and the perfectly straight line was gone. At no point was there a visible craft or object but there was an unmistakable, perfectly straight line being made through the middle of the cloud. It was like a vapor trail in reverse. I have no meteorological knowledge and as such I have no idea if this is something that just happens on its own.