Twenty million each, or threaten them with kriptonite which would work better?.
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I think that kryptonite would be ineffective, being as it only exists in comic strips. There is no Planet Krypton, nor is there any such thing as Kryptonite.
The original story was that all the folks on Planet Krypton had normal strength and were not capable of flight or other cool superpowers, because the Kryptonite on Krypton weakened them to normal human abilities, but once they left Krypton and there was no Kryptonite about, they had all these superpowers.
This does not explain why Superman's dad, Jor-El, is always drawn wearing a cape. Capes and spandex clothing are not that useful unless one is capable of flight.
In later episodes, Krypton tends to glow green and makes Superman very, very ill. The element Krypton does not seem to have anything to do with Kryptonite, since it is an inert gas. The creators of Superman apparently did not pay a lot of attention in their science classes.
In the film "The Incredibles" the costume designer mentions how capes are really not practical for even superheroes, and shows the demise of numerous caped ones being sucked into jet engines and having other fatal accidents as a result of their capes.
