1. Groot isn't so much a tree; he's more of a plant. You may think there isn't a difference, but James Gunn says that he sees Groot as a plant that has been evolutionarily geared towards forming a human-like sentient creature. Beneath that bark is musculature and veins, much "like a green, soft plant" which grows to fit function.

2. There were two on-set stand-ins for Rocket Raccoon. Sean Gunn — James Gunn's brother — did most of the on-set work as Rocket in the film. Arti Shah, a little person, was also part of the production, but she was actually too tall for the job. While Sean Gunn was able to crouch down to Rocket's height, giving his co-stars a proper eye-line, Shah had to wear an image of Rocket on her chest.

3. There are many special references and "cameos" in the Collector's "museum". One of them is a Dark Elf from Thor: The Dark World.