I remember this scene. Tigers routinely scratch bark of trees to either sharpen their claws and/or to scent mark. Before scratching the tree this tigress took time to smell the tree to ascertain the presence of other tigers. Since it was rainy season the scent marks get washed away. It is easy for us to watch it from a vehicle. Also these days these tigers have got accustomed to vehicles. In other places they won't be comfortable. So when I imagine Jim Corbett painstakingly moving close to tigers and watching them for hours, I wonder whether he was superhuman.