Actually, if you are only connecting the hot and neutral to the hot dog, and it is not touching any conductive grounded surface or object, the GFCI will not open the circuit.
I was only trying to supply a general idea for a lab. And I do not mean a labrador !! :roll:
Yes, the tin foil ( sunny side up
) would best be connected to an EGC. It may be more educational to see it fail. We learn best when things do not work as expected & we have to figure out why. At least I do. I also believe that experiments should be repeatable, they should all fail in the same way.
They could swap the wires into every possible combination to observe the result.