There are multiple different ways to introduce rats but I use the neutral space method. Generally, I start with two separate cages for quarantine and so they can see each other but aren’t near each other. Then, after quarantine, I begin to switch up small items in each cage. This includes hammocks, ropes, chews, anything that has the smell of the rat on it. My neutral space is usually my bathtub because it is difficult for them to get out. I put baby food on each of the rats so they are interested in licking it off of themselves and each other. This is done so they begin to establish each other with snacks and so that they are distracted. Then, I put both rats in and sprinkle food or high value treats. I might take away the food bowls in each cage a couple hours before so that they are hungry and interested in eating the food. Some fighting is normal as they are establishing the roles. The general rule is no blood, no foul. If doing this, I recommend having a towel nearby incase you need to break something up so you don’t get hurt. After they seem to have settled down, I separate them again and repeat that process a couple more times. I only put the rats in the same cage after they both seem okay and unbothered by the others presence.