Recently I got two rats from a lady who could no longer care for them. She had them for a week and I've now had them for two weeks.
Today the youngest (2 months according to past owner) was climbing the bars and I saw what looks like a bite on his stomach. I was thinking it was caused by the oldest (5 months) as I've seen him nipping at the other. They're both males and have plenty of hammocks but always sleep together and love on each other. They do wrestle a bit but it's usually just play.