Pilots on an Alaska Airlines flight from Mexico City to Los Angeles became (for lack of a better word) freaked out when Jewish passengers on their plane began putting on tefillin (small boxes that Jews tie around their arms with leather straps and which contain prayers). The plane was met at LAX by FBI and other law enforcement, who questioned the passengers upon landing. They decided they were simply religious Jews and let them go.
This is not the first time this has happened – last year a similar mix-up occurred on a US Airways flight to Louisville.
At this point, airlines should probably tell pilots that just because someone with a beard is saying prayers that they are not planning on blowing up the plane.