This is used as a term to describe someone in a position of authority who is corrupt, someone who will take money in exchange for doing something for the person paying that may be illegal.
If somebody is said to be once bitten twice shy, it means that someone who has been hurt or who has had something go wrong will be far more careful the next time.
When a sore is almost healed, and if a person rips or tears it open, it is way of preventing the healing process and further aggravating the pain. This phrase, metaphorically suggests, to revive or reopen a quarrel or enmity which was almost forgotten.
If you open a can of worms, you do something that will cause a lot of problems and is, on balance, probably going to cause more trouble than it's worth.
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