From the Journals of Commander Septimus Tiberius


One of the most famous of botched first contacts was our introduction to The Reptilians. We found several uninhabited planets with massive jungles that were suitable for colonization. After several months of surveying we found similar planets. All had thriving, diverse ecosystems. A perhaps higher than average number of large predator species. This was clear evidence of terraforming in some distant past. The Imperium Senate and House of Hands declared the grounds gifts from the Old Ones, clearly left behind for the Imperium to inherit.
Colony vessels were dispatched and several hundred acres of jungle was cleared to begin building initial settlements. Of course this was also a chance to test the Science Commission's latest batch of hyper-fertile rabbit slaves. Cloning is not efficient in producing the necessary populations to support an Imperium settlement. These clones were made to replicate organically through reproduction. We found newborns could be genetically and psychologically accelerated to be mature for labour in as little as six months. Females could only be made artificially and so the males could be kept in check by promised access to females at the height of their mating frenzy.
Now these settlements were not left alone. The Imperium left sufficient defense forces, nothing extravagant but enough to keep the slaves in line. There were no advanced civilizations anywhere near. We could not have foreseen what happened.

When an Imperium fleet arrived in time for the Rabbit's mating season, they found a Reptilian blockade around the planets. It was the Reptillians, who up until now had used the planets for their ritual wars. These wars happen at regular intervals on their sacred calendar, and normally they would fight among themselves. However when they found Mammalian settlements on their battle planets it fulfilled some great prophecy of great new enemies that would come from beyond. I remember seeing the great angular planet-cracker ships, and sun temple vessels that held miniature stars above them. I remember seeing how vast their fleet was. Their jump-gate technology was astounding.
On the planets below the war had already begun. We learned, during the ensuing war, that the Reptilians do not kill in battles. Despite this they are the greatest and fiercest enemy we have known. Our war with with them was not by any means assured and should we have to fight them again we will not underestimate them.
Prowess in battle is proven by capturing an enemy so that they might be sacrificed to their gods. A great honour evidently. Only warriors were killed this way of course. Though some rabbits fought and were sacrificed, most fled or hid. They were captured regardless.  Once the settlements were destroyed, the Reptilians began great feasts and fires. They culled the rabbits on gallows, hundreds of meters long according to reports. Some were used and kept, the Reptilians recognized useful slaves. Some were used, and hanged anyways. 
Some days I wish I could have been planetside. The Reptilians certainly know how to throw a feast.