"Stickers" are a byproduct of processing macadamia nuts for human consumption. During the drying process some of the nut kernels don't fully release from the inside of the shell. When the nut is cracked part of the kernel remains in the shell.
Stickers are great for parrot species that can't crack macadamia nuts themselves. They provide mental stimulation because the bird has to remove the remaining portion of the kernel from the shell, also providing somewhat of a foraging experience for the bird.
Note: During shipping, because of vibration and changes in temperatures, some of the kernels may release from the shells: therefore, you may find a few kernels without shells or a few shells without kernels. Additionally, I can't see the backside of the kernel. You may find a few with defects.