Report 58557: Dad and son take interesting photo after hearing possible wood knock and whistle while hiking near Denton

My son and I went trespassing up the Greenbelt Trail north of HWY 380, which has been closed for a couple years I believe due to flooding. A mile up the trail, we heard a distinct knock, though the distance almost made it sound like two rocks clacking together. My son also said he heard a whistle. As we retreated back to the parking lot, I snapped several pictures aiming behind me over my shoulder. One of the pics may have caught something interesting?  It appears, to me, to be a figure crouching next to a tree, with exposed skin on the face.