Them fakins don't bounce, unfortunately. .....and barely even move. It's the tell-"tail" sign.
I dated a Flight attendant (I used to love Flight Attendants before I moved on to nurses and then to Professors and then got married...thank god) who had salene implants that looked and felt unbelievably real. If it weren't for the sloshing I would hear at night, I'd never have known they were fake. They hung and moved like the real thing. It was truly unbelievable.