I use the standard clay flower pots for my hide. I don't know if the following technique would work on a glazed pot (probably not).
First, soak the pot in warm water for a while. The clay will absorb water and make it less likely to crack.
Second, once the pot is well soaked, put it upside down on a surface. Take a flat headed screw driver and a hammer. Put the head of the screw driver on the edge of the hole that is already in the bottom of the pot.
Third, carefully tab the screwdriver with the hammer. Gradually hit with more force until a piece breaks away. Keep breaking away pieces (keep them small) until the hole is the size and shape you want.
Fourth, smooth the edges. I use a coarse sanding sponge, but any kind of sandpaper will work. Just make sure the edges are smooth and not sharp. Be sure to sand the edges in side the pot as well.
I've made a few hides this way and my snake loves them. It's nice because you can make the holes bigger as the snake grows.
The clay pots are really nice because you can soak them for extra moisture when your snake is shedding. Plus they look more natural in the habitat than plastic (and plastic can have sharp edges when you cut it).
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