Subendometrial or junctional zone contractions (endometrial peristalsis):

  
This transvaginal ultrasound video clip shows the changes that take place in the endometrium of the uterus, in the immediate post-ovulatory phase or days immediately after ovulation. This patient underwent medication for induction of ovulation. The first part of the ultrasound video clip shows the endometrium on day 1 after ovulation- the endometrial stripe shows early secretory changes. But this ultrasound video shows another more striking feature- slow but definite waves of peristalsis (contractions) in the endometrium  proceeding from the cervix of the uterus upwards to the fundus. These waves of contraction are called junctional zone contractions or subendometrial contractions. It is believed that these contractions help propel the sperms upwards in the uterine cavity to enable fertilization of the ovum.
  Junctional zone contractions or endometrial peristalsis is most obvious in the immediate post-ovulatory period and decrease after that. During menstruation too, subendometrial and uterine contractions help propel the blood and endometrial tissue downwards; here the peristalsis is from the fundus downwards.
References: 1) Google books description of endometrial peristalsis
2) Textbook of ultrasound (google books)- subendometrial contractions
3) article on junctional zone peristalsis- Ultrasound imaging