The U.S. government has warned airlines to pay particular attention to the possibility of terrorists attempting to hide explosives in shoes.

The officials stressed there is no specific threat or known plot. Intelligence collected by the United States and other countries has indicated terror groups have been working on new shoe-bomb designs, the sources said.

 http://www.abc15.com/news/national/department-of-homeland-security-alerts-airlines-to-possible-shoe-bomb-threat