Apparently there’s only room for one black box per airplane.
From NY Daily News:
A Jewish prayer box worn by a teen passenger caused a Thursday morning furor on a flight from LaGuardia Airport, forcing an emergency landing in Philadelphia, authorities said.
The mix-up involved the 17-year-old boy’s tefillin, a black box filled with Biblical verses and tied with leather straps to his head, said Philadelphia police Lt. Frank Vanore.
What are Tefillin?
Also known as phylacteries, Tefillin are a “set of small cubic leather boxes painted black, containing scrolls of parchment inscribed with verses from the Bible, with leather straps dyed black on one side, and worn by observant Jewish men during weekday morning prayers” (WIKI on Tefillin).