Here are some tips / instructions to follow if you see a potentially dangerous animal:
1. Do not contact (touch) injured or unknown animals in any fashion. A bite from an animal may require immediate medical treatment for the injury or rabies. Immediately call animal control.
2. Keep children indoors and alert others.
3. For any animal bites seek immediate medical attention. Prevent anyone else from coming into contact with the animal.
4. Verify that someone has caught the animal before venturing outside. If someone is bitten, this animal will need to be tested for rabies and identified by emergency medical personnel in order to administer the proper treatment. Also, if the animal is a snake or a spider, it's crucial that medical staff be able to identify the species by actually seeing the animal. Inform the person catching the animal that the animal needs to be retained for identification purposes and transported along with the victim to medical staff.
5. If you feel an animal is a hazard to public safety, traffic safety like a horse blocking a road, cow, large animals, etc. call the police.
6. If you know the animal belongs to a friend or neighbor, and is not aggressive or dangerous, you may want to simply contain the animal in a fenced area and immediately notify the owner. Contact the SPCA if you are unsure who owns the animal.