A cyclist escaped injury after he was caught by the neck on a metal fishing line strung across the road.
The 31-year-old was riding along Tuckton Road in Bournemouth when he was caught on the wire and thrown into the road on Sunday afternoon.
Police said the wire was so thin that it was almost impossible to see.
"The wire could have seriously injured or even killed the cyclist - he could have been decapitated," said Sgt Mark Palmer, of Dorset Police.
Mindless act
"Whoever strung this wire across the road was acting in a mindless, reckless and extremely foolhardy way," he added.
"The cyclist was caught by the neck by the metal fishing wire and he fell into the road but luckily he suffered no serious injury.
"He sustained lacerations to his neck but he did not need medical treatment."
The incident happened near to the Belle Vue Road roundabout at about 1700 BST on Sunday and police have appealed for witnesses.
"The person or people who put the wire across the road may have bragged about it to friends, or let something slip to someone," Sgt Mark Palmer said.
"Dorset Police is treating this incident extremely seriously.
"If the wire had not injured the man, he could have been run over by other vehicles after being thrown off his cycle into the road after hitting the wire."
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