Cognitive biases occur when a character processes new information based on their personal ideas, perceptions, and experiences rather than viewing it through an objective lens. While biases are natural inclinations (the brain's way of simplifying and sorting through an overload of data) they often result in inaccurate interpretations, skewed conclusions, and illogical decision-making. 

It's important to note that bias typically occurs at the subconscious level, with the character being unaware of its existence or its influences on their thoughts and actions.

Eyebrows furrowing
Tilting or cocking the head
A flat stare
Pursing the lips or frowning
Shaking the head
Pulling at an ear lobe
Displaying restlessness (fidgeting, shifting position, pacing, etc.)
Slanting the body to the side
Putting their hands on their hips
Crossing their arms
Making assumptions
Making stereotypical statements
Waving a hand dismissively
Putting a hand up, palm out, in a stop gesture
Interrupting: No, that's wrong, Let me stop you there, etc.
Becoming confrontational
Squaring their shoulders or planting their feet
Talking over someone with a contrary view
Unconsciously taking a step back (or moving forward, if agitated)
Speaking with conviction (a sharp tone, directness, being emphatic, etc.)
Demanding proof or evidence when an alternative viewpoint is shared
Seeking information only from sources that agree with the character (confirmation bias)
Attributing bias to gut instinct: I tossed his resume because I had a bad feeling about him.
Glossing over information that contradicts their opinion
Applying tendencies or traits to a group of people based on specific criteria such as gender, race, nationality, religion, or age
Jumping to conclusions: They raised their prices? Talk about greedy!
Seeing a rare news event and believing it's more common than it is
Failing to see faults in certain people (favorable bias)
Giving someone (or a group) preferential treatment
Forgiving easily (being unable to stay angry)
Dismissing mistakes and missteps of those the character respects

Favorable Bias:
A feeling of expansion and warmth in the chest
Relaxed muscles, being at ease
A steady heart rate

Negative Bias:
The chest growing tighter
Body temperature rising
The stomach hardening
Breathlessness due to frequently interjecting or talking over people 
Tension in the muscles
A pounding heart

Sorting rapidly through existing knowledge to see how the new information fits in
Being conflicted; not knowing what to make of the information being presented
Giving greater weight to information that supports what the character wants
Thinking prejudicial thoughts about some people
Tending to believe or trust people who share the same views
Tending to disbelieve or distrust people who disagree with their views
Looking for ways to disprove those who disagree (instead of examining their own opinion to see if it's valid)
Having an us-versus-them mindset
Expecting an individual to behave a specific way because of a stereotype 
Being closed to new information that challenges the character's beliefs
Being overly inclined to see the good (or bad) in a situation 
Blaming external forces (instead of internal reasons) for personal failures
Viewing certain people as inferior
Applying deeper meaning to coincidental events
Forming opinions based on gut feeling rather than facts
Adopting opinions that are widely accepted by others
Making connections between unrelated events 
Believing that because something has never happened, it never will
Underestimating risks (because the character doesn't think they're a big deal)
Favoring certain ideas and decisions, even if they're not the best or "right" choices
Mentally justifying their thoughts so they can dismiss any suspicions of bias
Feeling self-righteous when someone responds as expected (because their bias is "confirmed")
Being annoyed when people disagree with them
Experiencing mental discomfort and wondering if they're being biased
Feeling like a bias might be in play but being unwilling to examine it too closely
Becoming defensive if someone suggests that the character is being biased
Waffling and second-guessing themselves

Going on the offensive; accusing a challenger of being biased
Searching for data, studies, and results to support their ideas (so they can feel right, rather than biased)
Surrounding themselves with people who agree with them
Avoiding environments where their beliefs will be challenged
Delaying a decision so the character has time to privately examine potential biases
Using noncommittal language: Well, I'll need to think about that.
Disengaging from the conversation
Changing the subject

Believe, assume, argue, demand, scoff, debate, claim, cling to, state, embrace, lean, view, filter, blame, expect, doubt, question, denounce, disprove, ignore, deny, suppress

AGITATION, ANGER, CERTAINTY, CONFIDENCE, CONFLICTED, CONFUSION, CONTEMPT, DEFENSIVENESS, DEFIANCE, DENIAL, DOUBT, FLUSTERED, FRUSTRATION, IRRITATION, NERVOUSNESS, RELIEF, RELUCTANCE, SATISFACTION, SCHADENFREUDE, SMUGNESS, UNCERTAINTY, UNEASE, VALIDATION

Staying open-minded
Forming an objective opinion
Making the most sensible and logical decision 
Viewing all people equally in terms of value and deserved respect
Doing what's right when it goes against a personal bias
Remaining impartial 
Fostering a welcoming and inclusive environment
Making accurate predictions about future events
Experiencing personal growth and becoming more self-aware
Accurately interpreting data
Respecting someone's choices when they don't align with the character's views
Solving problems creatively, which requires seeing situations from different perspectives
Supporting someone's decision when the character has personal doubts 

A situation with high stakes that requires an impartial decision
Someone accusing the character of bias (whether it's true or not)
Working or living with people the character is biased against
Someone else being put in charge because the character isn't trusted to think objectively
An experience that causes the character to recognize their own bias—especially if it's something they've been incentivized to embrace (as a political lobbyist, for instance)
The character voicing an opinion and being ridiculed for it
Acting on a bias and it ending badly for the character
Being called out for favoritism
Shedding a bias and having to confront those who instilled in (family members, an organization, etc.) 

Bias runs on a spectrum, and while we often focus on its negative effects, it can also skew to the positive, such as a grandparent viewing everything their beloved grandchild does in the best light. If, however, a bias activates and amplifies a character's darker emotions, their response could cause harm for themselves or others.