Definition of a Twin Bed

Now that the girls have been fully transitioned to big girl beds (and not just their cribs minus a wall "big girl beds) for over a month, we've stumbled across a minor hurdle.  Genevieve, who is much more the cuddler of the two, has developed a habit of finding midnight refuge in her sisters bed.  It's really from a sweet place, she just doesn't want to be alone.  But it's created a bit of a headache.  See, she doesn't just climb in and fall asleep; she climbs in and starts pulling at her sister's hair, tickling her toes or pinching her cheeks - basically anything she can think of to keep her sister awake with her.  What's become even more interesting is there's no fighting when she's discovered and made to go back to her own bed.  As soon as the door slides open, she climbs out of her sister's bed (often extending a hand so I can help her down), trots over to her bed and climbs up, lying down on her own pillow like it's no big deal.  It usually only happens once a night and it tends to come with in the first 20-30 minutes of bed time, but last night she did it at least a half dozen times, and as I was getting ready this morning at 5:30 she did it once again.  It's tricky on the monitor too, because it's hard to tell if that lump (either the one in Genevieve's or the second in Arianna's) is a baby or some other appropriate bed time companion (like sheets or a stuffed animal).  You kind of have to watch carefully and see if you notice a third arm move or a second head roll to the side.  I know they're called twin beds and all, but she doesn't have to take that literally!