Every year, thousands of whales strand — meaning that they wind up trapped on beaches or in shallow waters — and it’s really hard to figure out why.

It’s not for lack of trying. Teams of forensic researchers investigate stranded whales, studying organs, analyzing body parts with CT scanners, digging through stomach contents, and checking skin for scarring. But these meticulous whale detectives still often don’t find any answers.

“We can only about 50 percent of the time, if that much, give you a solid answer of why that animal died and why it’s stranded,” says Darlene Ketten, a marine biologist at Woods Hole Oceanographic Institution who refers to her work as “CSI: The Beach.”

One reason it’s hard to figure out how whales die is that scientists don’t know that much about how they live, Ketten explains on the latest episode of Unexplainable, Vox’s podcast about mysteries in science. They range widely across the planet and dive deeply. There are many things about their complicated bodies we don’t yet understand. And these researchers are often working with whale carcasses that have been decaying for days, which can distort the evidence left behind.