In 7 years of owning rats I haven't encountered this particular behaviour during intros. On Sunday I picked up a 5 week old hairless male rat to introduce to my group of 5 males. I've introduced 5 week olds no problem my whole time owning rats (in my country 5-6 weeks is the recommended age) and this group of boys have taken in new 5 week olds before without issues. 3 of the boys behave ok around the little new one, but they do continue to sniff him when they come across him, even though it's been 3 days of meetings now and I normally see them stop this behaviour way faster. One of the boys is overly eager to sniff the new boy's bum and will chase him around to do so, nonstop. There's been no grooming of the little one at all, just sniffing at him and there's been no bonding between any of them. My alpha has been eager to sniff him as well and he's been huffing at him several times so I've had to separate. Today he hasn't been huffing at him (yet) but he's been sniffing him and he's been nipping at the little one's face, what does this mean? Shortly after that he laid down close to the little one without problems. All of them will tolerate the little one sleeping next to them or even on top of them but then when they're wake they go back to this odd behaviour. I'm not sure how to interpret it. I've tried having both the overly eager boy and the alpha alone in a carrier with the little one and they'll behave well in there but then go back to the odd behaviour when they're out again. I don't see any difference in behaviour when they're on neutral territory or their usual play area. Is there any difference to introducing a hairless rat to a group of furry rats? Do they still smell the same? I feel like my boys are acting like they think this new boy is very strange and can't figure him out. I'm wondering if it's better to wait till the little one is maybe 6 weeks old and then try again? Should I continue introductions daily or take a break till the little one is a bit older? I feel bad that he's not accepted into the group yet and has to sleep alone. He's such a sweet boy and he has been trying to play with the other boys and he's been grooming the other boys but the favour just hasn't been returned.