Mary Sim's pet dogs are used to bolting their food - but they turned up their noses at a bag of Winalot.
Mary thought she was going barking mad when she opened the bag of dog biscuits - and found a ten-inch long bolt.
Mum-of-two Mary, 27, of St Andrew's Road, Didcot, said: "I was totally speechless."
It weighed 1lb on her kitchen scales.
Butch, a German Shepherd cross, and Rocky, a Staffordshire cross, were nut amused by the dinner delay, as Mary took the two kilo bag back to her local Tesco store.
And Winalot manufacturers Spillers Petfoods felt really ruff when they were alerted to the added ingredient in their product.
Company spokesman Evelyn Trundle told the Oxford Mail she had never heard of anything like it happening before.
"We are looking into it as a matter of urgency," she said.
"It is a serious matter, although at this stage there is nothing else I can say."
Oxfordshire Trading Standards Officer Graham Hill said it was possible that the bolt had come adrift from machinery and dropped into the bag during production.
The bag of biscuits and the bolt have been sent back to Spillers.
But Butch and Rocky aren't too bothered about the outcome of the inquiry, they're getting a replacement bag of biscuits to get their teeth into.
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