As crazy as it sounds, it makes sense, at least to me. See, let's say you have an empty hollow sphere that has no openings/holes, and it simply had gas, like air, normal air. Now, (speaking theoretically) if you were to squash the sphere until it's volume reached zero and then it turns inside out, right? Well, at the point it's volume is zero the volume of the gas is almost zero (it cannot reach zero volume otherwise it would just disappear, the reason the sphere can reach zero volume is because it is a shape, so at this point it is no longer 3-dimensional but it is 2-dimensional), the gas would have to fill the sphere up, and so as any gas would, it takes the volume of it's container. Here's the problem, with no volume, the sphere's capacity is zero, yet still has the gas inside it! Let's say the volume of the gas is V and the volume of the sphere is zero, since V is greater than zero, we can say V/0=infinity! Below zero volume, the sphere turns inside out, the gas is no longer in the sphere since the sphere is turned inside out.
If you're wondering about the V/0 thing, anything that is divided by zero will equal to infinity. E.g.: You have 8 slices of pizza and 4 children, 8/4=2. Now you have 8 slices of pizza and 0 children, 8/0=infinity. You'll essentially be cutting the pizza slices till the end of time to get enough slices of pizza to give, but since the children don't exist, you will never be able to give them the pizza slices.
Or, another theory (probably incorrect) is that the sphere is turned inside out, having a negative volume, but since it is turned inside out, it is safe to assume that since it's inside is outside, anything that was outside of the sphere became inside it, this basically means the entire effing universe. Everything, including black holes and whatnot. This sounds pretty crazy to me, so it's probably not correct. The previous theory is mathematically correct I believe, so yeah.
Guess what, this whole thought came to my mind when I was pissing, because I tried to imagine turning my bladder inside out, and this was what came afterwards. Took me about 30 seconds, because I had to quickly run back to my in-progress game of League of Legends.