For your safety, never put your fingers or objects other than paper into the shredder feed opening.
Many people underestimate the amount of paper they think they will shred. It is better to buy a shredder that is a bit too large than to pay high maintenance fees for a shredder that is too small and, therefore, overworked.
Feeding in more paper than the recommended capacity can cause jamming and damage to the shredder. Keep this in mind when shredding folded papers or heavier paper types such as cardstock or file folders.