contagious	(adj.) 會傳染的（easily spread from one person to another）；Laughter is contagious.
distinguish	(v.) 區辨、分辨（recognize the difference between two things）；Listeners could distinguish voluntary from involuntary laughter.
emerge	(v.) 出現、發展出（come out or start to develop）；Laughter emerged when humans began to live in groups.
engage in	(v phr.) 參與、從事（take part in）；Most primates engage in some form of laughter.
evolve	(v.) 演化、緩慢改變（change slowly over time）；These insects evolved over millions of years.
industrialized	(adj.) 工業化的（well-developed manufacturing）；People from less industrialized regions were better at the task.
innate	(adj.) 與生俱來的（natural from birth）；Involuntary laughter is an innate behavior.
origin	(n.) 起源、原因（the beginning or cause of something）；the origins of laughter
primarily	(adv.) 主要地（mainly）；Laughter is primarily a social activity.
threatening	(adj.) 具威脅的（showing the possibility that something bad will happen）；Chimp laughter signals the activity is not threatening.
adorable	(adj.) 可愛的（lovable）；A game of peekaboo sends babies into adorable giggles.
apparent	(adj.) 顯而易見的（clear）；It became apparent that there were differences between men and women.
assume	(v.) 假定、認為（無證據）（think something is true without proof）；Provine had assumed the pre-laugh comment would be funny.
bond	(n.) 連結、紐帶（connection）；Laughter creates a strong bond between parent and child.
bully	(v.) 霸凌、欺負（scare and threaten）；Laughing at someone can become a form of bullying.
episode	(n.) 一次插曲、事件（event）；Provine counted "laughter episodes."
humorous	(adj.) 幽默的、好笑的（funny）；Most laughter is not related to anything humorous.
purely	(adv.) 純粹地、完全地（completely）；Laughter has a purely social function.
tease	(v.) 取笑、戲弄（make fun of）；Laughing at others could be gentle teasing.
turn out	(v phr.) 結果變成、最後成為（happen; end up）；Even this kind of laughter turns out to be social.