I just got a new young female, I'm guessing about 3 months old, small but fully furry. I introduced her to my adult female rat, Penelope, who has lived alone for about a year and a half. Yesterday Penelope groomed the baby's ears and was fine, but today she kept tugging on the baby's neck and back, to the point where the baby squeaked a little. Is this aggression or is she just trying to groom the baby? Has anyone seen this happen before? Thanks!