Need Clear Defintion For Some Terms

this is a screen shoot from scott specialized catalog need to know what meant by "perf. intial " and "sensitive ink" did it mean anilin ink that is used in the printing of the stamp or what?

another question is what is the difference between normal perfin and precancel perfin and how to differentiate between them?

A perfin (short for perforated initials) is a form of cancellation. Sometimes it was done after the stamp was placed on a stock transfer document and sometimes before. After they are soaked off a document there is no way to tell whether the perfins were applied before or after placement on a document. Collectors do not and cannot differentiate between the two situations.

The sensitive ink was an experiment by the Bureau of Engraving & Printing and refers to the Series 1940 overprint and not the basic stamp.

thanks dear for your help with information