His arm had red swollen welts which he, unfortunately, spread to his belly when he drew his arm tight in an effort to stop the pain. Poor guy looked like he'd been flogged with a cat o' nine tails.
Will said it felt like he'd stuck his arm in an electric socket. This photo was taken about an hour later, after some of the swelling went down. We gave Will a Benadryl, and it seemed like the pain went away after about ninety minutes, and Will was fine the next morning.
Fortunately we were told that jellyfish are uncommon here, and we have had lots more swimming without further incident.