Yeah you can bounce yourself while a second person also bounces you at the exact same and so you are double bounced.
Alternatively, you can roll up like an egg while two other people try to bounce you and crack the egg. If two bounces manage to launch you a the same time then that also gets called a double bounce.
Both approaches to being double bounced are absolutely terrifying because you're feeling twice the force that you expected. So if you're an emotionally dead adult nostalgically looking back to the last time you felt something then the terror of being double bounced is a good candidate.
Well it's at a thrift shop so it's courteous to have the pieces in a bag because it implies that the complete puzzle is present when you decide to buy it or not.
If it's a used puzzle and the pieces are free range then it has the chance to be really disappointing when you can only learn it wasn't a complete board after you are 99.995% finished with it.