1. Personally, I’d take “一” as an intensifier of “探”, and it could be referred to “thoroughly” as an adverb in this case . You may also come across some other expressions related to 一探 on social media and books, as in 一探究竟 一探虚实 一探到底. But, we don't actually use these words quite often in our conventional conversation unless you want to sound formal on some occasions or harden the tone implying you're serious about whatever it is that's under discussion. 2. I wouldn't go so far as to say "为了一探内部" is a wrong expression here, maybe the translator was trying to be spoken, but if I were him, in this context, I'd be a little more inclined to frame the sentence like Summer did, i.e. 为了对内部一探究竟, which sounds more natural to most native speakers. In addition, sometimes we do hear people say 一探 XX to mean check out, figure out, for example, 我们来到伦敦 一探其城市足球文化 or 我们来到万里长城 一探其宏伟壮观. but, again, it's still a bit formal, if someone around me talks to me like that in causal conversation, I'd consider him/her to be pedantic. With regards to 缩, what kind of things can 缩 Other than 衣服缩水了/ 工资缩水了/ 气球缩小了/把图片缩小/公司的规模缩小了. You can also say 缩小范围 - to narrow down，字体/图片缩小 - to zoom out, 缩减 to reduce （数量）. When someone sticks his head/hand out of the window of a bus at high speed, the driver may tell him 把头/手缩回来（to draw your head/hand back） it's dangerous. Other expressions may be found as well, but I haven't thought of one yet. Hope it helps.:)

In order to take a deep look(一探) at what is going on inside, the egg should be magnified until its molecules can be seen. I think "放大” is more correct than "缩” here, but stand corrected. 缩 can be used for anything that is capable of becoming shorter,smaller or less.衣服缩水了/ 工资缩水了/ 气球缩小了/把图片缩小/公司的规模缩小了

一探is not a phrase，we often say一探究竟，means explore or figure out，一探in this sentense is the wrong expression ，为了一探内部，We can understand , the right sentence shounld be 为了对内部一探究竟/为了了解内部结构