It may be bigger on the inside than on the outside, like the TARDIS.
Like all dimensional physics, this can be best described in terms of a 2D universe (because you can't really imagine three dimensional space curved in a different dimension). Imagine the universe as a sheet. A small hole in the sheet in the bounty can. But under the hole the edges curve downwards into the third dimension, and out into a fish bowl or baloon shape. Remember that in a 2D universe you can only exist on the sheet, so in the space of the small hole is squeezed a much larger area. Now increase the power to a 3D universe (technically 4D- time). The hole is now the bounty can and the area of the fish bowl is now the volume of it. Easy.
Of course, I'm pretty sure that all this is beyond the technical advances on any Oddworld race, even with teleports (wormholes work on a similar way, however). That's why in my fan fic, the bounty hunter employs a Clakker who flies out his Meetle to shift the bounties back to jail (Stunks McCoy's Yolkswagon Meetle)
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