Rule, being a resin, will naturally get more length and give a more angular but strong arc. It saves a lot of energy and provides a huge backend reaction. The Animal on the other hand, will rev up quite a few feet earlier and give more of a smooth arc reaction. It doesn't cover as many boards and it won't give you a huge backend reaction, but it'll handle heavy-oil like a champ. The Animal's core is very strong and it revs up really hard in heavy oil whereas the Rule doesn't pick up on its roll as well. The Animal is definitely a true heavy oil ball. The Rule would be more for medium/heavy to medium. Both balls are excellent though!
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-Dino