Bolt cutters are easy to use, but can take a lot of strength to open, especially if rusty. Most people will probably use bolt cutters only a couple of times in their lives, such as when they've lost the keys to their bike or storage unit lock.
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First, check the safety latch.
If the safety latch is on, open it by twisting it to the left.
If the bolt cutters still don't open, get a can of WD-40, which can be found at any hardware store and some drug stores.
Spray liberal amounts of WD-40 on the hinge connecting the two sides of the bolt cutters.
Pull the bolt cutters apart.