Several patent laws, most notably that of the U.S., provide that the disclosure in a patent application must describe the best way of practicing the invention known to the inventor at the time of application. In effect, what this means is full disclosure; keeping the identity of a secret ingredient back or failing to tell about a detail that gets better results can invalidate the patent. The best mode is sometimes referred to as the preferred embodiment of the invention, though this may also refer to one of several embodiments recited in the patent, one of which must be the best mode. No best mode requirement exists under U.K. or EU patent law and failure to recognize this issue is a major pitfall for European patent agents when dealing with the United States. See Enablement.