Aggression vs Socializing

Rats are social animals, and as such, they will have all sorts of various interactions with other rats. When a colony - even as small a colony as two - lives together for a period of time, they establish dominance, social grooming, and play habits. New rats can disrupt the social order for a time until everyone figures out who goes where.

There are a lot of social interactions between rats which are perceived by humans as "mean," "bullying" or "aggressive." Most of the time, they are not - we tend to anthropomorphize our pets, because we like to believe they feel things in the same way that we do. They don't, though they are certainly capeable of strong feelings and emotions.

Boxing (standing on hind legs and slapping/pushing with front legs) - is a totally normal dominance interaction. It can be a prelude to aggression if done between strange rats, but it's usually a good way for rats to test their strength against others without having to hurt or be hurt. Usually rats are vocalizing while they do this, and most of their vocalization is too high-pitched for human ears to hear.

Wrestling - this can be a play activity, or a dominance activity. Rats can get scratched while tumbling and rolling around with one another, especially if they don't have a proper hair coat.

Puffing, hissing and side-walking - these are signs of serious dominance and a threat of aggression. This is a rat letting another rat (or a person) know they're willing to get into a fight and take it to the next level if they have to. This is sometimes accompanied by tail-lashing or banging, which is also a serious threat of stuff about to go down.

Side-rubbing - a rat rubbing their sides against the bars of the cage and wiping their hands on everything is covering the cage in his own scent. This is a dominant move, and a sign that the rat feels threatened socially by another rat.

Power-grooming - when one rat rolls another rat and then sits there nibbling through the other rat's coat, often accompanied by sad little squeaks from the groomed rat. This isn't an aggressive move, but is a dominance move, and should be left alone. In extreme cases, this can lead to the dominant rat barbering patches of fur off of the submissive one.

Squeaking/screaming - arguing (loudly) is a specialty of girl rats having a tiff, and doesn't necessarily mean anyone's getting hurt, contrary to what they sound like. If vocalizations are being accompanied by power grooming or wrestling, it is probably fine - accompanied by puffing, side-walking or leaping, and those rats need to be separated.

You should always take great care in separating your rats. Most of the time, it's best to leave them alone to sort their own problems out. You won't always be present, and by preventing an alpha rat from establishing dominance, you can actually force him into violence when you aren't around, because the submissive rats have learned that they don't need to submit.

If a rat is being injured by another rat, it's best to separate them right away. Do not do this with your own hands!! Try and place an object between them, such as a dustpan, and sweep them apart. Then take the calmer animal out of the cage and put them in a differnt one. Sometimes, two animals simply have such incompatible personalities that they cannot get along with one another safely. In the case of male rats, neutering often helps the issue.