In one case last September, a couple in Baltimore, Maryland, checked a plastic bag with a block of processed cheese taped to another plastic bag containing a cell phone charger.

Terrorists could be testing the system, or could be conducting repeated operations to desensitize security officials, the bulletin says.

While "initial investigations do not link them with criminal or terrorist organizations," the bulletin adds that "most passengers' explanations for carrying the suspicious items were questionable, and some investigations are still ongoing."

Cheese. They are on the lookout for Cheese. They have no evidence that the Cheese is connected with terrorism. But explanations for the cheese are "questionable." They are also on the lookout for devices that look like IEDs:

"The unusual nature and increase in number of these improvised items raise concern, and TSA personnel should continue vigilance for groupings of ordinary items that look like IED (Improvised Explosive Device) components," the bulletin says.

Like ipod chargers? I don't mean to make light of a serious situation, but the fact is that people who are professionally paranoid have a tendency to believe their own fantasies. When the TSA tells their employees to be on the lookout for blocks of cheese, they better have some credible reason. It doesn't sound like they do.

TSA to police: Look out for possible terrorist attack 'dry runs' - CNN.com