This article is from the WSSF 2013 AFRMA Rat & Mouse Tales news-magazine.

Patricia Cowley Brown, Facebook
QI am part of a forum (not rattie related) and someone was asking for rat advice. On there someone told her that a female rat could get pregnant while their cages were 6 inches apart. I have a lot of rat experience and degrees in Zoology and Biology and have never heard this happening. Is this even possible? She swears that it happened to the person in question twice.

Answer from Sariah Lily Jones, Facebook
APersonally, I think it’s far more likely there is a wild buck sneaking in at night, and/or someone let them play together without her knowing.

Then again, it’s not unheard of for a rat to escape a cage and then put themselves back in—all unnoticed as well! Someone I knew actually followed her escaped rat . . . saw her run back to the cage, go inside, and lock it; she’d been escaping and returning every night for about a week before they caught her at it. She had a drop-style lock which does tend to be easy for rats to learn to work.

Answer from Karen Robbins
AIt is not possible for rats to get bred from cages 6 inches apart. More like what Sariah Lily Jones said. Rats will do a lot of amazing things to get to the other sex like jumping off tables, climbing table legs, getting out of wire cages where they can force adjoining sides apart, chewing holes in plastic bottoms of cages, etc. Also, rats breed very quickly, and many times when rats are allowed to play together, that’s when babies are made.