I was helping out at a farm when I was in my preteens, and was rushed by a docile cow that loved being scratched behind her ears. I had petted and scratched her, and when I went to leave the paddock, she rushed me and almost impaled me with one of her horns. Since then I only have one working kidney.

Cows are big, strong and heavy, and docile dogs can also kill. Any kind of caution around things large or feisty enough to kill you is healthy.