Evolution of a brightening associated with the KHI. These are EUI 174 Å observations showing the difference between the observation at the given time and that at 05:58:52 UT. (a): development of ruffles at the interface between the jet and coronal plumes at 06:00:57 UT. The dashed lines in blue outline the boundary of the distortions of a ruffle. (b–f): evolution of brightening forming at the time when the ruffle reaches its maximum of distortion. The squares in white trace the location of the brightening from 06:01:02 UT to 06:01:27 UT.