I once encountered a huge metre long tortoise in the middle of the runway at Hargeisa, Somailand. Fortunately I was in a fairly short-landng aircraft and close to taxi speed before I spotted it - after a few disbelieving double-takes.
Shortly after another aircraft - I forget what but much bigger and faster made his traffic calls and I had a heck of a time explaining to him what the hazard was. He asked me if I could go and shoo it off the runway...!