During menstruation, the uterus sheds the endometrial lining
through vaginal bleeding. You might expect menstrual blood to look like ordinary red blood just like if you cut your finger. However, while the blood loss that occurs during your period may appear similar to any other blood loss, it can also look very different. Menstrual blood may be bright red, light red, or another color such as brown. Normal menstrual blood may be thin and watery, or thick and stringy. You may see clumps or clots of blood
during menstruation. This is part of the endometrial tissue and completely normal.
Getting Your Period; GirlsHealth.gov; http://girlshealth.gov/body/period.htm; accessed 09/09/07.