What causes lines in the middle of a 3d print? Solve under extrusion problems mid print, halfway up!

So annoying when you come back to a print that was going well to find these naughty missing lines in it. WHY DO THEY HAPPEN?! Well, underextrusion and a partially blocked nozzle obviously. But there's more to it than that. Possibly. No Eevees...were...harmed in the making of this video. Honest. Why are comments turned off? Because the vid is 4+ years old :) The basic principles of the video are STILL valid today but everything that needs saying has been said. Credits: Music: Ouroboros Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 3.0 License http://creativecommons.org/licenses/b.... The Lift by Kevin MacLeod Link: https://incompetech.filmmusic.io/song/5009-the-lift License: https://filmmusic.io/standard-license Voxel Revolution by Kevin MacLeod Link: https://incompetech.filmmusic.io/song/7017-voxel-revolution License: https://filmmusic.io/standard-license