In a Common Law system such as the one used in the US, law is interpreted to the letter and if something is not mentioned in a contract then it's considered undefined, no matter whether it's reasonable. So even though we can argue that sharpening the phone and stabbing yourself is a foolish thing to do, the law system pretty much requires them to explicitly mention these things or they may be held liable in court. This is also the reason why American contracts are so fscking long compared to most European contracts which follow Civil Law.
