Over time, soil will wash out through the bottom of the pot. If a vigously growing plant stays in the same pot for several years you could end up with a pot full of roots and not much soil, making it appear that the plant devoured the soil.

Here's an overview of how to repot.

1. Get some potting mix from your local nursery store. Note that you want potting mix for indoor container plants, not garden soil.
2. Remove the plant from its container and use a spoon or chopstick to knock as much of the old soil off the roots as you can...but be gentle and try not to damage the roots. This is messy so you'll want to do it outside if possible. You can discard the old soil in the trash or spread it out in your garden outside. If there are shriveled, dried up roots that come off when you pull gently, remove them. These are old rotted roots and you're better off getting rid of them.
3. If there's a clump of compacted soil in the center of the root ball it's important to carefully loosen this, taking care to minimize damage to the roots. The reason you want to remove these clumps is that roots cannot breathe in compacted soil.
4. Now that you've got the rootball cleaned off it's time to compare the size of the rootball to the size of your pot. You want the pot to be only a little larger than the rootball so that the roots have some room to grow, but not too much or you'll constantly have a layer of wet soil at the bottom. If the roots were completely filling up the old pot, get a new pot that leaves an inch of space all around the rootball. If the rootball is much smaller than the old pot, find a smaller pot. Be sure to use a pot that has an open drain hole at the bottom.
5. Your plant should sit in the new pot such that the top of the rootball is just below the rim. Hold it over the rim of the empty pot to get a sense of the correct height. As you're holding it there, start adding soil with a spoon or trowel. As the soil starts going over the roots, fill in the areas between the roots and in the center of the plant using your spoon. You want to fill in all the areas so that all the roots are contacting soil. You can gently tamp down the soil with your spoon or chopstick to remove air pockets but don't pack it. Your roots will need to breathe in there.
6. As the soil gets near the top of the root ball, continue tamping it down and continue filling with soil until it reaches the top of the rootball.
7. Thoroughly water until the water comes out through the drain hole. Keep the plant out of direct sun for a week or so. Don't water it again until the soil has dried out.

I hope this helps!