WATCH: A man fishing at Yellowstone National Park appeared unaware that a bison was approaching from behind until nearby visitors warned him of the massive anim

WATCH: A man fishing at Yellowstone National Park appeared unaware that a bison was approaching from behind until nearby visitors warned him of the massive animal. [▻](https://video.twimg.com/ext_tw_video/2081510838473494528/pu/vid/avc1/720x1280/jY8qryjM7vd_EW8J.mp4)