Some clues: "Both of them bought one-way tickets, paid in cash, both of them didn't check any baggage for a trans-Atlantic flight. They should have been subjected to a different level of search," Ron said.

Terrorism's ultimate goal

While he sympathizes with the concerns of flight attendants that knives and other objects could be used to hurt people, there are already objects in the cabin that mentally or emotionally disturbed people could use to inflict injury, said Richard Bloom, Embry-Riddle Aeronautical University's chief academic officer and director of terrorism, intelligence and security studies.

"That has nothing to do with terrorism," said Bloom. "Given that any organization, including the TSA, has only so many people and so much money, what they're trying to do is get less relevant things out of their attention and pay more attention to things that are more catastrophic."

An ever changing list of banned objects

The TSA's evolving list of banned objects has drawn mixed reaction from travelers.

"Let's allow knives on board, but you are not allowed a bottle of water, or a bottle of baby food," wrote one CNN.com reader.

Another seemed to take a more positive view: "I almost had my kids' safety scissors confiscated from their little activity kit. Yay for this sensible decision."

Commenter Jose L. Reynoso was more skeptical.

"Yeah sure one man against a bunch of others is no match but, what if ten men carrying knives and bats plot to take over? Wouldn't a massacre be obvious?" Reynoso wrote.

A more flexible aviation security system?

A country's security services need to be collecting intelligence on potential terrorists way before passengers board an aircraft, said Bloom. And any airport's security team needs to have flexible and layered screening in place to be able to adjust its processes for high-risk individuals.

"The threat is ever-changing."