特意请教曹老师：您好！

新编高级英语语法章振邦主编（2014年8月第4次印刷）170页:

说“情态助动词过去时形式还可以在以下语境中表示假设意义”，例如：

That she should forget me so quickly was rather a shock. (她竟会这么快地忘记我真令人震惊）

There is not the remotest possibility of anyone's calling upon me, and that I should call upon anyone else is a thing undreamt of.

(不可能有人来访问我，至于我去拜访别人，那是做梦也想不到的）

That I should see a college student arrested for stealing! (我竟然看到一位大学生因偷窃被捕，真是令人深思呀！）

Who would have thought that things should come to such a tragic end ! (谁会想到事态竟闹成这样结局！）

He stepped into a cave and what should he see but a tigress with her baby tigers. (她步入洞穴，你道他看见什么-一只母老虎，带着几只虎仔）。

......

我很不能理解以上例句，如何与“虚拟”“假设”“非真实”有关呢？

即以上例句，如何用“虚拟”“假设”“非真实”来理解，来解释呢？  句中哪里“虚拟，假设，非真实”了？

麻烦曹老师详细解释，谢谢！