I think Dave said some good things here. Keep in mind, we can't see for ourselves what is going on, so we have to try and visualize, and that's not always easy. I have bred Brazilian, and Peruvian Rainbows for several years. A male is usually the agressive one. If you have two males together and they smell a female in a nearby cage, they might fight. If you have another female and she is ready to breed, go ahead and put her in and see what happens. Check often because if you do have two males together now they may fight. I often have two males in with a female so they do fight. I have never had a male die, but they can get pretty violent, banging around the cage. Once the dominance is established, the dominent male will usually breed the female. Now if by chance you alreay have a male and female together, putting in another female won't hurt anything. He may breed one and then go to the other. I have found that boas don't always read the same books we do. Some rainbows like to breed in water. I always keep a 28 quart sweater box half full of water in the cage. They also like to soak after eating. Now, if you leave the big water tub in there after she is gravid, that is fine, but close to her due date take the tub out. Females will sometimes have their babies in the water, and some of the babies might drown. Yes, I have pulled dead babies out of the water, so I learned the hard way. I have never mis sexed a rainbow, but like Dave said, an adult male can sometimes be difficult. I bought a bci once, 7 footer, sold to me as a female. I probed it several times and it kept coming out to be a female. I threw the snake in a cage with a pair of boas and within minutes that she was a he. One of the best breeding bci I have ever seen. So it goes to show you these mistakes can happen, and I have probed hundreds of snakes.So, keep us posted, and good luck.