Watercolor paints tend to be rather opaque.

I'm assuming this is a true or false question. I would say the answer is false. Watercolor tends to be more transparent then opaque yet it also depends on a few factors. If someone uses a lot it then it becomes more opaque. If they buy a specific brand it may also be more opaque. There are many factors that go into this question but most of the time water colors are more transparent than opaque. 

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.