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.
Its guaranteed that this tool will make rewriting jobs a lot easier than before because you can finally take a rest and let the software do the job for you. This is a wonderful tool indeed, and rest assured that everything will be perfect as long as you only use this tool for the sake of rewriting articles and not for changing a content thats the same as the article that you need to write and not rewrite. Expect that you will be able to make things a lot unique for the rewrites that you do with the aid of this tool because you now know how big its database is.
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.
×