grows increasingly annoyed by and hypersensitive to another's repeated behaviors instead of growing more fond of his or her idiosyncrasies over time. Pheromones Certain pheromones secreted by animals, including humans, can attract others, and this is viewed as being attracted to smell. Human sex pheromones may play a role in human attraction, although it is unclear how well humans can actually sense the pheromones of another. Theory and aspects Chemistry In the context of relationships, chemistry is a simple emotion that two people get when they share a special connection. It is very early in one's relationship that they can intuitively work out whether they have positive or negative chemistry. Some people describe chemistry in metaphorical terms, such as "like peanut butter and jelly", or "like a performance". It can be described in the terms of mutual feelings - "a connection, a bond or common feeling between two people", or as a chemical process - "[it] stimulates love or sexual attraction...brain chemicals are definitely involved". A common misconception is that chemistry is an unconscious decision, informed by a complex blend of criteria. But in reality, chemistry is not a decision at all but a profound emotional connection between individuals that they can sense and feel on a deeper level. Some of the core components of chemistry are: "non-judgment, similarity, mystery, attraction, mutual trust, and effortless communication". Chemistry can be described as the combination of "love, lust, infatuation, and a desire to be involved intimately with someone". Research suggests that "not everyone experiences chemistry", and that "chemistry occurred most often between people who are down-to-earth and sincere". This is because "if a person is comfortable with themselves, they are better able to express their true self to the world, which makes it easier to get to know them...even if perspectives on important matters differed." Sharing similarities is also deemed essential to chemistry as "feeling understood is essential to forming relational bonds." There are various psychological, physical and emotional symptoms of having good chemistry with another person. It has been described as a "combination of basic psychological arousal combined with a feeling of pleasure". The nervous system gets aroused, causing one to get adrenaline in the form of "rapid heartbeat, shortness of breath, and sensations of excitement that are often similar to sensations associated with danger". Other physical symptoms include "blood pressure go[ing] up a little, the skin...flush[ing], the face and ears...turn[ing]