Liver and hydrogen peroxide lab results?

It's not stupid at all. I did this lab with my AP bio kids every year.
First, let's understand what happened in the hot water. We put pieces of chicken hearts or liver in the tubes and then did various labs.
When you heat or boil the water with the liver in it (or the catalase, also called peroxidase, which is in the liver cells), the heat causes the enzyme to denature, like putting a raw egg on a hot frying pan. When a protein denatures, it can no longer function, so once the enzyme is heated, peroxide should have no reaction because the catalase can no longer fit on the peroxide substrate molecules to break them down.
The cold water does not work as well, mostly because the cells within the liver do not have time to get cold enough for this to work. Unless you can freeze the liver for hours, it won't really work. In theory, the enzyme should not have worked, but in reality you are getting reactions from catalase in cells inside the liver, which are not cooled down enough to denature the enzyme. Heat is much more dramatic, and I stopped even trying with the cold reaction. The theory is right, but the liver really needs to be frozen through to see the results properly.
Also, we'd wait for the bubbling to stop completely and replace the old liver with a new piece, and there would be no reaction at room temperature. This is because the substrate, the peroxide, had been totally broken down and all that was left behind was simple water, which does not react with the enzyme.
Here is the reaction:
2H2O2 + catalase= 2 H2O + O2
It is the escaping of the oxygen gas that causes the bubbling. Peroxide is a poison to the cells, which is why we have enzymes to break it down and is why it works as an antiseptic. It kills bacteria and the bubbling of the escaping oxygen helps to clean out dirt and bacteria from the wound.