I was having a bit of a surf around Blogland and came across this amazing graphic by Material Mama, which shows how a sewing machine works to combine bobbin and needle thread. I think it's brilliant as well as strangely compulsive viewing: well worth a look. Some clever folk have managed to embed the graphic into their own blogs but I can't work out how, so I've linked it instead.
Nutmeg aka MaterialMama also links to this, which is more techy but less hypnotic. I believe these images will fascinate my family, who are used to sharing their home with sewing machines, accompanying accessories and essential stashes but also appreciate the hows as well as the whys.