So what happens to Jimmy during all of this? [ _author’s note: *hits blunt*_] Well if his [that being Mr. Jimmy World,] volume doesn't change, his density would indeed skyrocket. Human beings have a density close to water of about 1 kg/liter so a typical Canadian male, who has a mass of 80 kg has a volume of about 80 liters. Once the mantle is eaten Jimmy would have a density of [55 sextillion] kg/liter and by the end about [75 sextillion] kg/liter or about 75,000 trillion tons per teaspoon.

This would cause Jimmy some problems. For one, that density is greater than the density of a neutron star (up to about [1 quadrillion] kg/liter) in which the nucleii of the atoms that make up the star are all smooshed together with the electrons and protons all forced together to make neutrons. So there's not enough room inside of Jimmy for all the matter that he ate no matter how much you compress it, assuming it stays as normal matter. You can solve that one by assuming that Jimmy is feeding a black hole (in the astronomical sense) in his stomach. That black hole grows as he eats and at the end of the meal the black hole will have grown to about 1.8 cm across.

Feeding a black hole is really the best way because as you go deeper and deeper in the Earth, the thermal energy contained in Jimmy's meals gets greater and greater. The last bite of iron core provides him with an extra 300,000 joules or so of energy as compared with his first sip of water. Luckily we can store that all in the black hole without anything coming out. But if Jimmy doesn't have an interior black hole, he is going to need to get rid of that energy. That means he will start to emit radiation. At first he would feel himself getting hotter and that radiation would be thermal radiation. But as he continued to eat the radiation would get more and more energetic. Before long he would glow a dull red color before getting brighter and brighter and whiter in color before he began to emit X-rays and finally deadly gamma rays, killing anyone who got close to him.