Ever seen inside a prepared piano? I hadn’t either. Here’s what it looks like when you’re doing the preparing:
There’s a table in Cage’s Sonatas and Interludes that lists what strings you’re supposed to shove stuff in and how far from the bridge the stuff goes. Insert a screwdriver, twist to spread the strings, and in goes the plastic or rubber or screws or bolts. Of course, Cage’s measurements were all for one specific piano, so you end up adjusting after you insert them.
And there’s what it looks like afterward.