The US airline Delta is working with the FBI and officials in the Netherlands to find out how sewing needles entered in-flight meals.
The needles were found in sandwiches on four US-bound flights that left Amsterdam on Sunday.
Delta spokeswoman Chris Kelly said in an email to Reuters that the sandwiches were prepared by the airline's Amsterdam caterer, Gate Gourmet.
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"I saw a lot of smoke come out from the tail-end of the aircraft. I wondered if it was normal, whether it was just exhaust fumes."