Get Down! It's A Fruitcake!

From the TSA website 2004 Holiday Season Travel Tips:

Do not pack heavy food items in your checked luggage. Foods such as fruitcake may cause the airport screening machines to alarm, thus slowing down the security process.

Communication intercepts have suggested an increased traffic in citron and candied cherries, but no specific targets have been identified.

I bet you could take out a cockpit door with one of those things, if you could throw it hard enough.