Sans is laid back, often sleeping on the job and taking breaks. His laziness is a combination of fatalism and apathy. He wonders if his indolence stems from his knowledge that any progress he makes will be erased when the timeline resets. Conversely, he suggests that this knowledge could be "a poor excuse for being lazy." Though Sans is usually agreeable, he becomes eerily serious at particular moments. He is also observant; Sans reads the protagonist's expressions and can often tell when they have already done certain tasks. He enjoys making skeleton-related puns and the fact that he performs at MTT Resort hints that he may be a talented comedian. He enjoys science fiction and loves to drink ketchup. He also hates making promises. Sans may have a scientific background. Evidence includes the quantum physics book, workshop, his relationship to Alphys, affinity for science, and his timeline research.