Cyclists could have been seriously hurt by fishing line found tied across cycle paths, police have said.
At least one man was injured after he struck the fishing line on a cycle path in Marston, Oxfordshire.
Thames Valley Police said it could have been much more serious if the man had been travelling at speed or struck in the throat.
Police condemned the vandals who laid the traps across a series of cycle paths on Monday and Tuesday.
Insp Stuart Gibbs said: "This may have just been a Halloween prank but I would like to stress that this is extremely dangerous behaviour."