Glancing down, he noticed what looked like a sewing needle in the food. Another passenger on the plane reported the same thing.
At first, he thought a toothpick meant to hold the sandwich together had punctured the roof of his mouth. When he pulled it out, "it was a straight needle, about one inch long, with sharp points on both ends."
Now U.S. and European authorities are trying to determine how the needles got into meals served on at least four Delta flights from Amsterdam to the U.S. and why anyone would place them there.
"We are keeping all options open because at this moment, we have no idea why somebody or something put needles inside the sandwiches," said Robert van Kapel, a spokesman for Amsterdam's Schiphol airport.
The FBI and the airport's police department have opened criminal investigations. The U.S. Transportation Security Administration said it does not view the matter as a threat to national security.
A Delta Air Lines Inc. spokeswoman said the needles were found Sunday in six sandwiches on four flights. Passengers discovered four of them. The flights included one to Minneapolis, one to Seattle and two to Atlanta.
Tonjes was returning home after a visit to Amsterdam for his mother-in-law's 90th birthday. The nine-hour flight was about 90 minutes from Minneapolis when flight attendants offered Tonjes, who was seated in business class, a cold Mediterranean salad or the hot turkey sandwich.
"I'll be very honest, the first bite, I thought, 'Boy, this is pretty good,'" Tonjes said. "It was the second bite that got me."
Now Tonjes is on a 28-day course of pills (at a cost of $1,400) aimed at warding off any infection, including hepatitis or HIV. His doctors have asked the FBI to tell them right away if they find any residue on the needle.
The sandwiches were made by Gate Gourmet, one of the world's largest airline caterers, with facilities on five continents.
The company serves many airlines, but only Delta flights appeared to be affected. The company said it was investigating. Spokesman David Fisher declined to elaborate.
Gate Gourmet was founded in 1992 to cater Swissair flights and grew by taking over other airline caterers, including that of British Airways. It went into private ownership in 2003.
Even though U.S. airlines no longer serve free meals in coach on domestic flights, the airline catering business is still a big industry. Gate Gourmet provides food for 9,700 flights per day. That's 250 million meals a year from 122 flight kitchens.
Those kitchens are often not on airport grounds, so meals are taken by truck to a "sterile" area where planes are parked. Security is supposed to be high. The TSA monitors the area in the U.S. Local authorities monitor it at overseas airports.
"Food delivery to airports is a very strict process," said Erroll Southers, a former FBI agent who was the chief of Homeland Security and Intelligence for the police department at Los Angeles World Airports. Truck drivers get background checks, and "those trucks are inspected for everything from sealed packages to explosive devices," said Southers, who is also managing director of counter-terrorism at TAL Global Corp., an international security consulting service.
The needles are a reminder that insiders - people who work within the industry and have passed a background check - are among the biggest threats to aviation security, Southers said.
Gate Gourmet's ads for cooks say applicants must be able to pass a criminal background check. The TSA declined to discuss the security process.
Ton Scherrenberg, chairman of the VNC union that represents some 7,000 Dutch cabin personnel, said cabin crews check prepared food for foreign objects when they open catering packages on board aircraft, "but you can't check every single sandwich."
When the needles were discovered on the first Delta flight, a message went out to other Delta flights, which is why some of the needles were found before they got to passengers. The TSA said it "immediately notified all U.S. air carriers with flights from Shiphol to ensure awareness."
On board Tonjes' flight, he pushed the flight attendant call button as soon as he found his needle. A few minutes later, another passenger nearby did the same thing. He said flight attendants offered to call ahead for an ambulance.
"When we landed, it was very, very impressive. When they opened the door, it was flooded with customs agents, police, paramedics and firefighters. It was the whole jetway full of people."
The FBI interviewed him for about three hours. He said he was told the remaining sandwiches were X-rayed, and a third needle was found.
Gate Gourmet was cited by the FDA in 2005 for failing to keep meat at proper temperatures and for the presence of live flies and roaches near its salad production area, plus other violations.
Roy Costa, who runs food safety consulting firm Environ Health Associates in Deland, Fla., and used to be an auditor with the Department of Health and Human Services for more than 20 years, said food preparation standards are not as tight in Europe as in the U.S.
"Everything we do over here, we do because the (Food and Drug Administration) requires it," he said. "There's just a huge hole there."
Associated Press writers Doug Glass in Minneapolis, Mike Corder in the Hague, Netherlands, and Samantha Bomkamp in New York contributed to this report.