This is a video of musician Mattias Krantz replacing all the strings inside an upright piano with guitar strings to hear what it will sound like. SPOILER: a piano that’s had all it’s strings replaced with guitar strings. Duh! “You get beat up a lot don’t you?” I’ve never been to a bar and it not end in a fight.
Keep going for the video, but skip to 7:15 if you just want to hear the result. The video after that is of piano strings on a guitar, skip to 1:30 in that one.