A picture of two brothers with their hair standing on end taken in 1975 shows what can happen just moments before lightning strikes.
Electrical charges in the atmosphere - responsible for lifting the hair - can be a warning sign that lightning is about to hit.
This old picture is featured on the blog of Michael McQuilken, the 18-year-old on the right, who had no idea that he and his brother, Sean, 12 years old at the time, were in danger.
The pair had gone climbing at Moro Rock in California's Sequoia National Park with their sister Mary, 15.
Michael, now 56, told NBC: "At the time, we thought this was humorous. I took a photo of Mary and Mary took a photo of Sean and me. I raised my right hand into the air and the ring I had on began to buzz so loudly that everyone could hear it."
They then felt the temperature drop and decided to return back down the mountain.
But a bolt of lightning struck minutes later, and Sean was hit. Recalling the moment, Michael told NBC: ""I found myself on the ground with the others. Sean was collapsed and huddled on his knees. Smoke was pouring from his back."
The picture has now come to light again thanks to John Jensenius, the lightning safety specialist for the National Oceanic and Atmospheric Administration, who discovered McQuilken's blog post about the incident and shared it with a wider audience in a bid to help keep people safe from lightning.
According to the Daily Mail, an average of 54 Americans a year died as a result of lightning strikes between 1982 and 2011.
But, thanks to safety work and awareness-raising like that of Jensenius, deaths are on the decline, and there were only 26 lightning fatalities in 2011.
What to do if you hair starts standing on end this way? Seek shelter immediately, advises Jensenius, adding: "If that's not possible, squat low to the ground on the balls of your feet, making yourself the smallest target possible and minimise contact with the ground."
Last week, a mother who was struck by lightning escaped with just pins and needles thanks to her husband's wellington boots.
Deborah Kendall was putting her two-year-old daughter in her car during the thunderstorm when she was hit by a bolt near her home in Smalley, Derbyshire.
Speaking to the Daily Telegraph, she said doctors told her "the fact I was wearing David's wellies may have insulated me and stopped the lightning from earthing."
Terrifying moment couple's Florida beach wedding struck by lightning
Ryanair flight struck by lightning diverts to Glasgow