I have trouble feeding my LO. Sometime when he gets it he really gets it and does this too. He doesn't throw up or get gassy afterwards so I think it's fine. I'm using Dr. Brown's bottles.
My LO does this too...and I'm using the VentAire also. I tried using the Nuk bottles, but even tho it was a slow nipple, I think it was too fast for her anyways...she always spewed I think it's fine!
Re: gulping hard on the bottle?
Our DS does this when he's upset and hungry.