The expression “can of worms” is an increasingly popular phrase in English meaning “a source of unforeseen and troublesome complexity.”
The phrase originated in the United States in the 1950s when bait stores would sell cans of worms.
The fishermen that bought these cans found them very easy to open and yet they were surprisingly difficult to close. As a result, there was a good chance that the worms would take advantage of their newfound freedom and escape.
Nowadays the expression is used not only to apply to a literal can of worms, but also to anything that unexpectedly becomes troublesome and complex. This expression is commonly used in conversation or in writing to refer to a topic that could possibly become very complex and start an argument. Here is how it would be used.
I talked to my friend about how his singing was very annoying and hegot mad at me. I could have told him that his mother-in-law gives voice lessons, but I did not want to open that can of worms.
The title of this article is another example of how this expression is used:
http://www.guardian.co.uk/world/2010/feb/03/iran-launches-rocket-carrying-animals
The article says that Iran’s rocket launch proves that it can be technologically superior to the West.
The idea that the West is technologically superior has been widely promoted for years and any challenge to this idea could have unpleasant consequences. Therefore, Iran’s rocket launch, according to the article has opened a can of worms.
