Terence Mace spotted and posted on Twitter two of the same pages listed in the Google search results from Google because Google seems to have misconfigured their hreflang and canonicals.
The query is done on Google.co.uk for [google crawling and indexing] and up comes the first two results on listing the google.com page and the other the google.co.uk page for how Crawling & Indexing works at Google.
Here is a picture:
Google hates, absolutely hates, showing the same result twice in the search results. Typically, Google handles this even without canonicals or hreflang implementation but in this case, nope.
I guess even Google makes mistakes.
Forum discussion at Twitter.