Neighbor disputes often stem from small things: unwieldy tree branches, garbage that's piling up, a barking dog.
They happen all the time, experts say — but they don't often end in broken ribs, like the one between between Kentucky Sen. Rand Paul and the homeowner who lives next door did.
"Normally it's verbal abuse," Victor Merullo, a Columbus, Ohio, based attorney specializing in tree and neighbor law, said. "To drive someone to a physical assault has to be something significant."
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Paul was mowing his lawn in his gated community in Bowling Green, Kentucky, last Friday while wearing headphones when he was allegedly attacked by Rene Boucher, a 59-year-old doctor who has lived next door to Paul for 17 years, sources told NBC News.
Related: New Details on Rand Paul Assault: Sneak Attack, Mystery Dispute
The motive for the attack is still unclear. Jim Skaggs, a member of the Kentucky Republican Party executive committee who lives in the neighborhood, said Paul and Boucher had a long-time disagreement that may have started political and turned petty, possibly influenced by trash or leaves being blown onto Boucher's lawn.
"Sometimes you make best friends with your neighbors, and sometimes you don't. Neighbors are people, and people have disagreements."
While there are no apparent statistics tracking neighbor disputes across America, Paul is far from the only one who's ever been at odds with his neighbor, the experts say.
"Sometimes you make best friends with your neighbors, and sometimes you don't," said Samuel Tamkin, a Chicago-based real estate attorney. "Neighbors are people, and people have disagreements."
The type of dispute is often dependent on the kind of property the residents live in, he added. In high-rise condos, for example, smoke wafting from one unit to the other or noise from the floor above are common complaints.
In single-family homes, trees are often the issue, Tamkin said: roots encroaching on a neighbor's foundation, or branches that overhang onto a neighbor's property. Boundaries — questions over where one property ends and the other begins — are common in larger properties, he said.
Unlike disagreements that happen in public places, neighbor disputes often stem from deeper issues, said D.G. Mawn, president of the National Association for Community Mediation. His organization has community mediators in more than 200 locations nationwide who are trained on bringing parties together to work out conflicts.
"Generally that dispute between neighbors is not just about the dispute. There's something underlying, some past history, some emotion," he said. "Many times the issues have to do with issues of respect, feeling disrespected, issues of self-determination and feeling others are impinging on that."