These fish yawn — and it’s contagious

ape: A group of rather large primates, all of which lack a tail. They include gorillas, chimpanzees, bonobos, orangutans, gibbons and humans. Most people tend to group humans into their own separate subcategory owing to a number of special traits. These include a larger brain, greater mental abilities (including being able to talk) and their ability to walk on two legs.

artificial intelligence: A type of knowledge-based decision-making exhibited by machines or computers. The term also refers to the field of study in which scientists try to create machines or computer software capable of intelligent behavior.

behavior: The way something, often a person or other organism, acts towards others, or conducts itself.

biologist: A scientist involved in the study of living things.

cold-blooded: Adjective for an animal whose body temperature varies with that of its environment.

ethologist: A scientist who studies ethology — the behavior of humans or other animals, usually within their natural environments. For non-humans, such research would usually focus on the behaviors of animals in the wild.

freshwater: A noun or adjective that describes bodies of water with very low concentrations of salt. It’s the type of water used for drinking and making up most inland lakes, ponds, rivers and streams, as well as groundwater.

mammal: An animal distinguished by possessing hair or fur, the secretion of milk by females for the feeding of their young, and (typically) the bearing of live young. They also are warm-blooded (or endothermic).

primate: The order of mammals that includes humans, apes, monkeys and related animals (such as tarsiers, the Daubentonia and other lemurs).

psychologist: A scientist or mental-health professional who studies the mind, especially in relation to actions and behaviors. Some work with people. Others may conduct experiments with animals (usually rodents) to test how their minds respond to different stimuli and conditions.

species: A group of similar organisms capable of producing offspring that can survive and reproduce.

unique: Something that is unlike anything else; the only one of its kind.

warm-blooded: Adjective for animals (chiefly mammals and birds) that maintain a constant body temperature, typically above that of their surroundings. Scientists generally prefer the term endothermic to describe animals that generate heat to control their body’s temperature.

zebrafish: A small tropical freshwater fish belonging to the minnow family. Zebrafish are used frequently in scientific research because they grow quickly and their genetic makeup is well understood.