The thing on the tree stopped us cold. One moment we were laughing along a quiet forest trail; the next, we were staring at a huge, twisted mass that looked disturbingly like a brain.

Nobody could explain it, and every photograph deepened the mystery until a search back home finally revealed the startling truth behind that bizarre forest grow…

Comparing our pictures with images online pointed to something called a tree burl: an unusual woody growth formed when a tree’s normal development becomes disrupted. Injury, infection, or other stresses can be associated with these formations, although their precise cause isn’t always clear.

The rounded swelling and tangled texture that had baffled us were consistent with a natural growth, not an animal’s nest or something someone had attached to the trunk.

Burls can remain on trees for years, sometimes becoming enormous.

Beneath their rough exterior, their twisted grain can produce intricate patterns prized by woodworkers. But discovering one in the forest is a reason to look, not cut: removing a burl can seriously damage the living tree. For us, the answer didn’t diminish the wonder. It changed it. We had walked past countless trunks expecting ordinary bark, only to discover how much there still was to notice along a familiar trail.