woodchipper
A woodchipper is a machine used for reducing wood (generally in the form of tree branches or entire trunks) into smaller woodchips. They are often portable, being mounted on wheels on frames suitable for towing behind a vehicle. In popular culture, they're infamous due to their use in the 1996 Coen brothers film Fargo.
Needless to say, sticking your arm, foot, head, or anything else in one is a very bad idea.
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This tag implicates shredder_(machine) (learn more).