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7 Nudges & Manipulative Techniques present in Undertale

This brief article will highlight 7 major manipulations found inside Undertale, and how they influence the player's experience.


In order to successfully engage the audience and deliver the desired aesthetics, games take advantage of specific processes peculiar to the human mind. Influencing the player means keeping control, and the degree of this condition is ultimately decided by designers.

Part of the success of the indie RPG Undertale resides in its skillful control of in-game mechanisms and information. The aim of this article is to present 7 cognitive biases and psychological effects, providing game examples observable inside Toby Fox’s most successful videogame.

1. Norm of Reciprocity


People tend to return positive treatments and ignore or repay with hostility negative ones.

This social norm states that we pay back what we received from others, creating a network of obligation. Reciprocity is universal, and stand at the very roots of human society. The social pressure created by this effect can also lead to an unbalanced interaction between the parts: an initial favor can be followed by an action with a bigger positive effect. Moreover the urge to reciprocate decreases over time.

There are three main types of reciprocity:

  • General reciprocity, with limited expectation of a future reward.
  • Positive reciprocity, balanced or unbalanced (between the parts).
  • Negative reciprocity, balanced or unbalanced (between the parts).


In the opening segment of Undertale the player can experience this nudge:

  • Flowey presents himself as a positive guide with useful tips and friendly intentions.
  • Within a minute from his first appearance on-screen he reveals his murderous intent.
  • This encounter solidifies the image of Flowey as an insidious antagonist in the mind of the player.

The game as a whole subverts the norm of reciprocity with its pacifist ending, and can be seen as a critique of the law of retaliation.

2. Hawthorne Effect


Individuals tend to modify their behavior in response to their awareness of being observed.

Observing or judging human subjects can alter their actions due to the attention they are receiving. The extent of this alteration is linked to the feedbacks received from the observer: explicit intents can lead to a stronger alteration of a subject’s behavior.

Three other main factors can arise concurrently with this effect:

  • Demand characteristics. Displaying clues of the expected behavior can increase the likelihood of it happening.
  • Novelty effects. Be under experiment can lead to an initial increase in performance.
  • Performance feedback. Increased attention from the observer results in increased performance feedback.


After leaving the Ruins the player is observed by a mysterious presence, which will turn out to be Sans the skeleton. Two elements are used to trigger the desired effect:

  • Sound effects and eerie music.
  • Repetition of the trees, both in background and in foreground.








Characters that break the fourth wall, such as Flowey and Sans, can also modify the behavior of the users, judging their actions.

3. Apophenia


Human tendency to perceive meaningful connections between unrelated things.

It can also be described as "unmotivated seeing of connections accompanied by a specific feeling of abnormal meaningfulness". Apophenia refers to our inclination to see patterns and meaning in random information. This bias can arise from various inputs, especially from complex topics and vague data.

There are four subcategories of apophenia:

  • Pareidolia. Seeing visual patterns in random visual information.
  • Gambler's fallacy. Perceiving meaning in random numbers.
  • Clustering Illusion. Looking at large amounts of data, people tend to see patterns in it.
  • Confirmation bias. Testing a hypothesis under the assumption that it’s true.


W.D. Gaster and the legends created around his figure are a perfect example of this bias:

  • The only certain information is that he was the predecessor of Alphys, responsible for creating the Core inside the Hotland.
  • There are three NPCs, that can only be seen during certain runs, whose dialogues contain hypothesis about his disappearance.
  • He doesn’t have an officially known form, the community tend to believe that this sprite (found in the game files) represents Gaster. Looking at the sprite upside down can trigger the pareidolia effect: the pattern on his body can be perceived as a second face.
  • He’s commonly associated with Sans and Papyrus due to his name and aspect.







4. Selective Perception


Individuals tend to perceive specific information based on their particular frame of reference.

People automatically interpret sensory information in a way that is congruent with their beliefs. This tendency is linked to the high number of stimuli experienced by humans, in relation to their needs. Selective perception distorts human judgment, causing an ignorance of opposing viewpoints.


During the course of the story these are some of the elements that tend to be erroneously perceived:

  • Name of the main character. At the start of the game the player assumes that the name given to the fallen human refers to the main character, whose real name turns out to be Frisk.
  • EXP and LV. Commonly known as “experience” and “level” from an RPG perspective, they instead stand for “execution points” and “Level of Violence”.

5. Mere Exposure Effect


People tend to develop a preference for things that are more familiar to them than others.

Humans tend to prefer easy cognitive processes over complex ones, for this reason they stick with familiar things. Repeated exposure increases familiarity, and familiarity reduces uncertainty. Ultimately, this phenomenon makes understanding and interpreting easier.


Undyne is introduced to the player through a combination of mere exposure and gradualism:

  • At first she is mentioned by Papyrus as a fearsome authority of the Royal Guard.
  • After entering Waterfall she is presented in a dim light, with her full armor on.
  • Before the Garbage Dump she unleashes two spear barrages against the player.
  • Undyne appears two more times in the presence of Monster Kid before revealing her fish-like aspect and facing the human.

6. Category Size Bias


The relative size of a category has an effect on its perceived value.

Utilizing this bias, games tend to convey the level of danger that the player is going to face. Incrementing the visual size of an obstacle, in relation to its group, leads to a perceived higher difficulty: for this reason bigger bosses are generally associated to bigger challenges. A visual and numerical categorization can also create a contrast between a minor group, made of bigger and stronger bosses, and a major group of smaller common enemies.


The addressed phenomenon is especially true for the last four main bosses of the neutral run, and it's generally applicable to a selected category of bosses and enemies:

  • The sprites of Papyrus (aspiring Royal Guard), Undyne and king Asgore reflect their position and the threat posed.
  • The king’s trident is red and stands out as a deadly weapon, Undyne’s spear remains white. These weapons are linked to their roles.
  • Flowey’s godlike status is represented by his body, made of a cluster of rendered images. His appearance sets him apart from the rest of the monsters, evoking a dichotomy between organic tissues and mechanical components.

7. Nostalgia Effect


Feelings of nostalgia weaken the desire for money, instead fostering social connectedness.

Nostalgia is an independent emotion, a sentimentality for the past that enhances positive self-regard and provides existential meaning. It has a powerful and long-lasting effect on human decisions. This emotion increases the perception of a social network in which we belong and our urge to spend money.


Undertale posses different elements that can arouse this emotion:

  • The pixel art and the color palette, similar to the ones used in the 16-bit era.
  • Visual and auditory references to games such as Mother, Shin Megami Tensei, Tomba!, Mario Paint and many others.
  • Toriel motherly attitude and places with familiar or melancholic atmosphere: the Ruins, Snowdin Town, Waterfall area, etc...

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