Just because other animals eat them does not mean that mushrooms, berries, or other things are safe for humans to eat. Many creatures can eat things that are toxic to us.

We can also eat things that are toxic to other animals. For example, chocolate and onions are both toxic to dogs, but are safe for humans to eat.

Also, it is not unusual for an animal to eat something that is not good for it. For example, birds will eat a Monarch Butterfly, but it is toxic enough to make them sick. Once they eat one, they will never eat another. The only way to know if a fungus, plant, or animal is edible is to identify it, and research its edibility.