In all three games, Rocks exist throughout your town, in numerous amounts from 5-10. Although they seem to be there for no reason, once a day, one of those rocks will turn into a Money-Rock, that when hit with a spade or axe produces free Bells.
 Money Rocks
Once a day, a rock in a town will turn into a money rock. If hit by an Axe or Spade, bells will fall out of it. As soon as it is hit, an invisible counter will start, stopping in about 5 seconds also stopping any more money from coming out of the rock. (Varies between games).
To avoid the knock-back you get when hitting a rock, stand in front of the rock and dig holes to the left and top (If you are standing on the north side). Any objects in the path around the rock (Trees, fruit, other holes, etc) will stop some bags of money coming out.
Money rocks aren't the only scenery item which, can provide money, the other item is the money tree.
In Animal Crossing, one rock in your town will give up to 13,300 Bells, being three bags of 100, three bags of 1,000, and one giant bag of 10,000 bells.
In the second game Animal Crossing: Wild World, the chosen rock in your town will give out up to 8,500 bells. These come in bags of 100, 200, 400, 800, 1,000, 2,000, 4,000 Bells, in that order. Yellow Feng Shui may allow for an 8,000 bell bag to appear.
The rock in Animal Crossing: City Folk plays much like the Wild World, except with one exception. You can now receive bonus bells by using a Silver Shovel, this tool has a small chance of doubling the amount of bells you receive from a single bag.
It is possible to find bugs under rocks and to capture them with a net. Play must hit the rock with either a shovel or an axe which, may have a pillbug or a centipede crawling out from under the rock. Player should immediately attempt to capture the bug because it will eventually disappear.
In all games, after the fourth or fifth bag sprouting, the next hits will be joined with the "One-Up" tune from the Mario Bros. games.
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