"They said, 'Don't worry. It stopped being active,'' the 14-year-old actor continues, adding a comic pause (you can tell that Jaden shares his dad's sense of humor). "That didn't really take away the worry."
A volcano wasn't the only thing Jaden had to get used to on set. There were also snakes, wild pigs and a curious monkey who almost made a cameo (Will tells a funny story about that in the clip above). The crew included four snake wranglers who swept each new location before filming.
We expect to find the famous father and son in more exotic destinations in the future. "Costa Rica just gives the film a very eerie size and scope," says Will. "At this point in my career I figure I'm going to start choosing the movie based on the location."
For more on Jaden, Will and After Earth, check out our live video Q&A with Jaden!
Gallery | Jaden Smith's Photo Timeline!