What should not be done when heating a liquid in a test tube over the Bunsen burner flame?

If you would cover the end of the test tube with a paper towel, there is a big chance that the paper towel will also catch flames. If the liquid inside the test tube is flammable, the type of flames that it can form may be larger than usual. This can lead to some accidents inside the lab.

It is a good thing that students and professionals are always taught about the proper lab rules and regulations. Only people who would think that this can be done as a joke may try it out. All of the other choices are things that should be done while handling a test tube.