Non-Newtonian fluids are amazing. Most of us have played with them at some point, but few have actually experimented with it. Currently, non-Newtonian fluids are a major research vein for body armor in how they can be flexible until a large force impacts the material, at which point its properties would cause it to solidify and (in theory) stop a bullet.
Does the theory hold water? Yes, it does, but Silly Putty itself is not the answer as Taufledermaus kindly shows.