So, first of all, baby raccoons were even more adorable than Peter had realized. (Mantis's shriek of delight could be heard all over the ship.)
Second: baby raccoons bite. Hard.
Peter couldn't figure out exactly how smart Rocket was at this age. The tiny, masked ball of fluff was definitely brighter than the average baby raccoon, but he was also distinctly ... well ... animal-like, bristling and hissing and puffing up his fur whenever anyone came near him, and fleeing into the darkest, most hidden part of the ship he could find. Which was most of it. Peter thought they were never going to get him out of the ventilation system, but Gamora lured him out with bits of food, and once they made him a little nest under the bed in his quarters -- containing a blanket and a handwarmer cannibalized from a cold-weather suit so he had something warm to cuddle up to -- he ended up spending a lot of time there.
It made dealing with him a lot easier once Peter managed to shift mental gears from "winning the trust of the child version of my friend/brother" to "taming a wild baby animal". However, baby Rocket also liked to steal bits of technology from all over the ship and collect them in his nest (electrical parts, gun components, explosives, even Peter's Zune a time or two) which didn't really strike him as normal raccoon behavior.
Peter wasn't sure why, but it somehow seemed to matter to him to get Rocket to trust him. He spent hours lying on the floor in Rocket's quarters (and frankly, the floor of Rocket's quarters wasn't a fun place to be), holding out a hand with tidbits of food, or just talking to him quietly while Rocket watched him from under the bed with bright, wary eyes.
"I know you've been hurt," Peter said softly. "No one on this ship is going to hurt you. I promise."
He couldn't tell if he was getting through. He couldn't even tell if Rocket understood a single word he said. He kept right on wondering until the time he woke in his darkened quarters with something small, warm, and solid tucked into the space between his forearm and hip.
Peter went very still and looked down at Rocket, who'd crept onto his bed while he was sleeping and curled up in a tiny furry ball against him.
Hesitantly he cupped his hand around the baby raccoon and went back to sleep.