If you’re driving through Christian County, Missouri, you’ll need to pay extra attention to the roads — even if they appear to be empty.

Local police have discovered make-shift road spikes on several local roads. The spikes were created by hammering large files into the pavement.

According to the Christian County Sheriff’s Office, “the first set was located on Aspen between White Ash and Harris. Another set was located on Aspen just south of Green Ash.”

It’s extremely difficult to notice them, as they were inserted following the flow of traffic.

Take a look at the Sheriff’s Office’s Facebook post below.

Christian County Sheriffs Office found these inserted in the roadway today between Nixa and Highlandville. These are…

Posted by Christian County Sheriff's Office on Sunday, December 20, 2015

Police don’t know who’s behind it, and have not yet determined a motive.