Any article rewriter or paraphrasing tool basically scans through the content you provide it in order to look for all the words that it can replace with suitable synonyms or substitutes. Every replaced word will appear bold and highlighted in a colorful text. Clicking on the word will give you details such as original word or other suggestions, you also have an option to add your own word. By clicking on the original word, you can go back to original.
So what does PARAPHRASE (or rephrase) exactly mean? It's a fundamental way of meaning analysis of sentences, developing, changing one's thoughts, the content of a specific text, for example, two evoked sentences: "father saw how a neighbor talked with mother. My father saw my mother talking with the neighbor" express the same content, but they are structurally different. The system of functioning in the language is valid. It is also reworking or rephrasing the work that contained the content, complementing it and interpreting it sometimes with a lot of freedom, but in the bounds that ensure a clear recognition of the original. Paraphrase is also a communication tool that serves, among other things, to confirm the level of understanding of what has been said. Rephrasing is most often made in the form of longer speeches, therefore only general sense and utterance are given away. In Coaching, the paraphrase is a useful tool, although, like many things, it ceases to fulfill its function in excess. Paraphrases are most often used by a coach when he wants to understand the client's statement more closely and thus show that he is actively listening. Paraphrasing includes: free conversion of a literary work; developing, reworking, rewording and describing a given text, preserving the meaning of the message; it's piece which is a free transcription of the borrowed subject; adaptation; modification of a work that changes form, not content; processing or variation of a literary work. Remember, that paraphrasing is not the same thing as summarising. Summarising occurs when you provide an overview of a topic or give an overview of the author’s key ideas as a whole. A summary is usually way shorter than the original piece of writing and it might state the ideas of a paragraph in one simple sentence.
Imo it is not possible for google to detect properly spun content, it is not worth computing power it requires. They can do this using ngrams for example, but it is uses a lot of queries. And for example article spinner I coded beats this algo, so google cant detect that the content is spun. Manual spinning is also good but it takes more than 30 minutes per article.