I first caught this on Bruce Schneier's blog:<p><a href="https://www.schneier.com/blog/archives/2015/04/shaking_someone.html" rel="nofollow">https://www.schneier.com/blog/archives/2015/04/shaking_someo...</a><p>He points to a great xkcd cartoon:<p><a href="https://xkcd.com/538/" rel="nofollow">https://xkcd.com/538/</a>