Hi Jassy. Gizmo is being a bit of a bully, huh?
What he is doing is completely normal. He is just posturing. It's what he should be doing. I would be a bit surprised if he didn't
do anything to show his angst. He'll get over it.
He will soon want to play with the baby and you will swear he is killing her if you watch. Dart is doing the same thing with baby Jude here. He puts Jude's whole head in his mouth. Jude lets him know when he gets too rough. Dart lets Jude know too when the shoe is on the other foot.
Just a wee bit of a caution. When you bring the baby back from the vet please do another day or two of intros again. The baby will smell different than before the vet visit and, if she gets shots, she will need the rest away from an exuberant big brother anyway. She's a bit young at six weeks for shots though. Most vets like to wait till they are at least 8 weeks.
Another word of caution for when she gets a little older. She will not have had the "training" she needs on how to play properly being taken away from mom so early. Make sure when you are playing with her you use toys and not your hands or they will look like mince meat.
Congrats on the new baby!!!