I am sure it's anal glands. Dogs have these glands just inside the rectum. They normally excrete a little every time the dog has a bowel movement. They are a scent gland basically.
When they are expressed, they are empty for only a short while as the body produces more fluid to fill them again. When a dog gets scared, they can empty them just a little or a lot. It can also happen when they get excited also. I used to have a American Staffordshire terrier. She would empty her anal glands when she vigorously barked sometimes, if they were really full.
They can be surgically removed.
When they are expressed, they are empty for only a short while as the body produces more fluid to fill them again. When a dog gets scared, they can empty them just a little or a lot. It can also happen when they get excited also. I used to have a American Staffordshire terrier. She would empty her anal glands when she vigorously barked sometimes, if they were really full.
They can be surgically removed.