I do wonder, and this is a serious question.  Why would someone trying to be deceitful because they have something very serious to hide even take the chance on speaking with a security agent?  I&#x27;m not suggesting they &quot;plead the fifth,&quot; but rather carry a card explaining that they are mute.  Doctors papers are easy to forge.<p>If the incident leading to the condition happened recently, then that would be an excuse for not knowing sign language.  Yes, they may still need to write their answers, but it is universally accepted that most people don&#x27;t like to write so they could keep their answers brief without raising suspicion.  By writing slowly, they may even drive the interviewer to the point they cut the questioning short.  Very serious bad guys could even get a botox injection beforehand, paralyzing their lips or get their mouth wired shut.<p>My point is that at the end of the day, the goal here is to catch very serious bad guys.  Any truly dangerous person with the intent and actual capability to do something very bad should have tools of deceit on par with their capabilities for harm up to and including getting one&#x27;s mouth wired shut.  Note that for this discussion I&#x27;m discounting &quot;shoe bomber&quot; types as not really having a capability for harm.  I suppose that at the end of the day, that&#x27;s who techniques like these are aimed at in the first place.  Alas, there is no such thing as perfect security.