Lightning during a recent thunderstorm appears to have killed six cows in Queensland, Australia last week, the Beaudesert Times reports. The cows were discovered days after the storm — dead and bloated, lined up against a metal fence. The bizarre incident is a reminder that while lightning strikes may be rare, they’re also deadly — particularly for big animals like cows.

The ranch owner’s son, Derek Shirley, discovered the four cows and two calves when he surveyed the property after the storm. The cows had been dead for enough time to have puffed up and rolled onto their sides with their legs in the air. But none had any marks on them, Shirley told the Australian Broadcasting Corporation.

The timing made lightning a likely suspect. It’s happened before; lightning killed 323 reindeer in Norway in August 2016. “It isn’t that unusual to see farm animals, or wild animals such as reindeer, being killed by lightning,” lightning safety expert John Jensenius with the National Oceanic and Atmospheric Administration, told The Verge’s Angela Chen at the time.

COWS STRUCK BY LIGHTNING BEAUDESERT Has anyone seen anything like this before? Four cows and two calves have been found dead in a paddock in Beaudesert, they’re all in a line and there isn’t a mark on them. What happened? Dr Karl explains: http://ab.co/2tqqmDf Posted by ABC Brisbane on Wednesday, March 7, 2018

Most lightning deaths, particularly mass livestock deaths, are caused by the ground current. That’s the energy that radiates along the ground after lightning strikes a tree, or the ground nearby. If you — or, say, a couple hundred reindeer — are standing in the wrong spot, at the wrong time, that energy can travel through the ground, up one leg, and down the other. As that electrical current travels through the body, it can stop the heart, Jensenius told Chen. And the farther that electricity travels before it leaves the body, the more damage it can do, according to the National Weather Service. So big animals like cows or reindeer are especially at risk.

But it’s also possible that the metal wires on the fence conducted the electricity — zapping the cows huddled along it. While metal doesn’t actually draw the lightning, according to the NWS, metal objects can become a conduit for the lightning’s energy. “Whether inside or outside, anyone in contact with anything connected to metal wires, plumbing, or metal surfaces that extend outside is at risk,” the NWS says.

Livestock deaths can be hard to track, so we don’t actually know how common events like these are, Jensenius said. But we do know that fewer people die from lightning strikes these days than they used to. In the 1930s and ’40s, between 300 and 400 people in the US were killed each year by lightning. Over the past ten years, the number has dropped to an average of about 35 people per year in the US. To keep those numbers down, these latest lightning deaths are a good reminder to get inside during thunderstorms and stay away from anything that can conduct electricity — barbed wire fences included.