Signed a legal document in support of an open source initiative against patents that had a section that was confusing and hard to understand. I remember thinking it was probably no big deal and anyway the document was for a good cause.
A couple years later that section had legal consequences almost derailed a major transaction involving our company. We could have avoided the whole thing by checking with our lawyer first. Moral of the story: never sign any legal document you don't understand.
Not responding is also an action. Just assuming it's safe to ignore a C&D without understanding possible risks would not be my first choice. For instance it would be helpful to know if you need to seek out additional legal counsel which is potentially time-consuming and expensive.
A couple years later that section had legal consequences almost derailed a major transaction involving our company. We could have avoided the whole thing by checking with our lawyer first. Moral of the story: never sign any legal document you don't understand.