The flood of weapons uncovered by airport screeners continues to grow, despite repeated warnings by the Transportation Security Administration.
In May, the TSA discovered a record 65 firearms on passengers in one week, including 45 loaded guns.
The TSA is now seeing a surge in a new, harder-to-detect weapon: credit card knives.
The weapon looks like a thick credit card but becomes a knife with a steel blade once the blade is folded out. The remaining section of the card snaps together in the shape of a handle.
So far this year, the TSA has discovered 491 credit card knives on passengers, through the use of metal detectors and full-body scanners, said Ross Feinstein, spokesman for the TSA.
That averages to about 20 card knives per week.
TSA officials declined to guess why the knives are showing up at airports.
The knives are sold online for $4 to $15 from various retailers. Iain Sinclair, a British manufacturer of one of the most popular devices, describes them as "lightweight surgical knives" that can cut through seat belts in case of emergency. The company could not be reached for comment.