For bipolar in adults, I think there's pretty good agreement about what this looks like. For bipolar in children, there is some considerable debate about where are the boundaries. At the mild end, are these just kids who are active? Is this the class clown at the very severe - is this something other than a mood disorder?
In interior decorating, the pig's actually quite there. It's used in paint for the texture, but also for the glossiness. In sandpaper, bone glue is actually the glue between the sand and the paper. And then in paintbrushes, hairs are used because, apparently, they're very suitable for making paintbrushes because of their hard-wearing nature.