Injuries which damage the brain are one of the most serious which can be sustained in any accident. Brain accidents most commonly involve either a "closed head injury" which is a hard bang to the head where the skull is not broken, or a "penetrating injury" which is where an object is able to directly enter the brain and cause damage. Closed head injuries most often occur when the head hits a surface with some force, but without damaging the skull itself. This type of brain injuries are also relatively common in sports accidents and automobile accidents. They can also occur when the head is shaken too hard, for example when a baby is shaken. They can cause concussion and sometimes bleeding inside the brain, known as "compression". Other types of brain accidents lead to the brain being penetrated by an object, for example if a person receives a stab wound to the head. Occasionally this may occur without breakage of the skull, for example if a penetrating object passes through the eye socket. Some brain accidents involve the actual damaged bones of the skull itself penetrating the brain and causing injury and can result from hitting the head so hard in an accident that the skull is broken.