Wis. Stat. § 346.11: Passing or meeting frightened animal.

Whenever a person riding, driving or leading an animal which is frightened gives a signal of distress to the operator of a motor vehicle by a raising of the hand or otherwise, the operator of the motor vehicle shall promptly stop the vehicle unless a movement forward is necessary to avoid an accident or injury and shall, upon request, stop all motive power until such animal is under control.