(as in sewing, not faecal matter)
believe it or not, but i do actually own a sewing machine - and i can even operate it (if not exactly well).
it's a relatively old elnita 150, and the only electric bits in it are the motor and the light bulb. i do admire the mechanical design of mechanical sewing machines: two cam drums, a comb full of cam followers, a few levers, a bunch of springs. in this machine that's enough for 15 different stitch patterns.
however, mine doesn't get used often. today i wanted to prep it for some upcoming fiddly fabric work, only to find out that it would only zig spastically, not zig and zag.
after applying occam's razor to isolate the involved ziggy bits it turned out that the issue was just stiffened old grease and/or insufficient lubrication: one follower lever had gotten too sticky to return properly when released. for zig that one gets pushed but for zag it needs to return under spring tension, which it didn't do reliably.
the solution was trivial; a bit of fresh light oil, some soaking
time and vigorous exercise of the mechanism and it's all working
again. me happy