Having watched it, it is ink

To be totally honest with you, I did not even notice the red line under the alligator. Not sure how I overlooked that. Rewatched and looked into it. The red line, admittedly unfortunately positioned under the alligator in the thumbnail, is just a golf course thing marking off a water hazard on the side of the course.

I also made the link send people directly to the fox part of the video, which is after the alligator part.