13 week ultrasound

One of the perks of being pregnant with twins is the string of ultrasounds. With a singleton pregnancy, the OB can just listed to your belly and record the heart rate, but for twins, since you can never be sure whose heart is whose, these frequent heart checks are done by ultrasound.
When Jason and I went in for our 13 week ultrasound, we found out that the bebes had been busy over the weekend and had managed to completely change positions (which they will do a lot in the coming months). They are now in a very cute face to face position. We watched in real time as the two of them gently squirmed and "looked" into each other's cute fetal faces....soooo cute....then all of a sudden, one of the bebes winds up and delivers a quick punch to his (her?) womb-mate, right in the face! Jason started laughing hysterically and I was dumbstruck. The target bebe (who's just floating around in there with no real resistance) fell backward. Bebe's first stunt scene? The OB assured us that it's normal twin bebe behavior, go figure!