But, seriously folks.
If you think about the physics involved, the answer should be obvious. Even a small, silk hanky will be held in place by inertial forces, gravity and the air resistance on the back of the hanky. It will take a finite amount of time for the hanky to overcome these forces and move backwards enough to allow the bullet, traveling at several hundred feet per second, to pass under the hanky without cutting the threads. Without doing the math, it seems obvious that could not happen, and that the projectile will cut the threads faster than the hanky can respond.