It had been discovered that the book was a palimpsest, and beneath the surface writing on the manual script laid, guess what? Mathematical theorems and diagrams from Archimedes.

网友在这个句子末尾漏掉了句号。

红色部分为一个完全倒装句。beneath the surface writing on the manual script为前置的介词短语作地点状语。laid在此被用作不及物动词，说话人为了进一步突出主语，在谓语动词后作了停顿，并让读者或听话人猜测主语是什么。然后在guess what？大写给出一个名词词组说敏这就是主语——Mathematical theorems and diagrams from Archimedes.

在非正式英语中，lay常被一些人当作不及物动词lie使用，本句中的laid就是被当做不及物动词用的。《韦氏高阶》对这种用法说明如下：

lay

4 [no object] informal : to be in a flat position on a surface : lie

• The book was laying on the table.

◊ The use of lay to mean “lie” occurs commonly in informal speech but it is regarded as an error by many people.