Natural behavior of a single artificial intelligence or even entire groups is a great challenge but also necessary for the immersion in video games. The object of this work is to find and implement the best technique for the behaviors of the simulated people in "Cosmonautica," Chasing Carrots' next game. The comparison of the different decision-making techniques shows that behavior trees combined with utility functions are the best choice due to their overall composition of flexibility, quality, performance, re-usability, and maintainability. Now, behavior trees are used in "Cosmonautica" to control the behavior of crewmembers in the player's space ship. They determine e.g. in which situations the crew members work or when a need has to be satisfied. Utility functions are used to compare all possible actions to decide which work task or activity needs to be done. This combination of behavior trees and utility functions has proved to be an easy and powerful way to control the behavior of artificial intelligences.