Mound
The dirt on the forehead of a pig makes a small mound. Picture it, if you will. A pig is rooting through the dirt. It lifts its head and there is a mound of dirt right on its forehead.
Imagine that you're the pig. How big can you make your forehead dirt mound?
ちょう
つか
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The pig's forehead dirt mound keeps getting bigger until it's the size of two cars (つか)! Pigs are big, but you didn't think one could balance a mound the size of two cars on its forehead and not fall over.
Picture a pig with a mound of dirt the size of two cars leisurely stomping around on a farm.