Proof, of Something

The following if from my friend, Tom:

In the current new yorker briefly noted book reviews they review a book about Hitler's private library (he read a book a day, they say). They don't think the book adds much to our knoweldge of Hitler, but the review concludes with:

"...but Hitler's reading yields few new insights, and some of what Ryback dredges up is merely peculiar: between the pages of an early acquisition, a guidebook to Berlin, is 'a wiry inch-long black hair that appears to be from a moustache.'"