300 .repro splits a bot in two by copying itself (mitosis) when a number > 0 is stored in it.
.repro is the simplest and most widely used reproduction method. This will allow a bot to reproduce an exact duplicate of itself. The number stored in .repro defines the percentage of energy and body to transfer into the child. Like all reproduction methods this takes a single cycle, after which a new bot is produced directly in front of you (ie: eye5) and facing you.
While the eyes begin working immediately for the newborn, it takes a cycle before the refs begin reading back. This can cause wasteful attacks by the child, a good idea then is to limit the child's firing until at least one cycle of age.