4. In an experiment pubished in 1988, social psychologist Fritz Strack of the University of Wurzburg in Germany asked volunteers to hold a pen either with their teeth—thereby creating an artificial smile—or with their lips, which would produce a disappointed expression.

【分析】复合句。句子主干为 social psychologist FritzStrack ...asked volunteers to hold a pen...。句首的介词短语作整句话的状语；either with ...or with... 作动词 hold 的方式状语，第一个状语后的现在分词短语作目的状语，第二个状语后 which 引导非限定性定语从句。

【译文】1988年发表过一项实验，德国维尔茨堡大学的社会心理学家弗里茨·斯特拉克和他的同事们招募了一批志愿者。他们让一部分人用牙齿咬住一支笔，从而在脸上制造出“人工笑脸”；或是用嘴唇叼着笔，从而产生“沮丧表情”。

5. Those forced to exercise their smiling muscles reacted more enthusiastically to funny cartoons than did those whose mouths were contracted in a frown, suggesting that expressions may inflence emotions rather than just the other way around.

【分析】复合句。主句为 Those... reacted more enthusiastically to funny cartoons，过去分词短语 forced to...作后置定语修饰 those。than 引导比较状语从句，该从句中的主语 those 由定语从句修饰，因其较长，谓语又因与主句重复而省略为 did，所以用倒装语序。suggeating... 为现在分词结构作结果状语，其中包含 that 引导的宾语从句。

【译文】那些用牙齿咬着笔，表现出笑容的人比那些用嘴唇叼着笔、表现出沮丧神情的人在看搞笑的动画片时所作出的反应更丰富。这就证明了表情能够影响情绪，而不是情绪影响表情。

【点拨】1) contract 作名词时意为“契约，合同；婚约”；作动词时意为“缔结，订契约；染上（恶习，疾病等）；（使）收缩，（使）紧缩”。2) frown“皱眉，蹙眉”，既是动词也是名词。