The thing used to fake this result may be consumed almost entirely and remain undetected after the test.
***In other words, something chemical. All known chemical reactions have been accounted for.
How so? You said the demos weren't scientific.
So you don’t think it should be checked before the experiment, if I was the customer I would demand it.
I would call BS, nothing is ruled out till it is checked.
Why only check after the experiment? What are you afraid of?