How the gelatin is prepared can affect the result.
Explanation:
To perform this experiment efficiently, you need to prepare the jelly made from fresh fruit and the jelly made from canned fruit equally. That's because if you modify the ways of preparing the gelatins, they will show many differences and you won't be able to tell if this difference was caused only by the nature of the fruits, or by the way of preparation. Therefore, the way the gelatins were prepared can modify the experiment result and leave it imprecise and unreliable.
For starters, humans have feelings and cells. If we get hurt we can feel things such as pain unlike a tent. If you hit a tent there is nothing it feels because it has no feelings. We have cells all through our body and rocks don't. They are made of other stuff but not cells.