Shaking, especially from a novice, is from the release of tension. Post-flop, you can generally place them on a hand and play accordingly. But pre-flop they cannot have a made hand and the release is nothing more than the all-in bet. And the all-in bet doesn't tell you much more than a call. If they are holding monsters, you still have a ~30% chance to reduce the field. Folding is likely to wise the novices up to the fact that you are stealing their blinds, and shows weakness that will invite agressiveness from the short stacks.