(CNN)Whether it's comics and sneakers, or books and art, collecting is largely seen as a normal, if occasionally obsessive, pastime.
Morbid and macabre: Dark obsessions of the world's most extreme collectors
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But what can be said about those who collect all things macabre -- fetus skeletons, taxidermy mutant farm animals and say, the personal effects of jailed serial killers?
"Morbid Curiosities: Collections of the Uncommon and Bizarre" gives a closer look at these more unconventional collections and the people behind them.
Rather than writing them off as eccentric provocateurs or disturbed misfits, writer Paul Gambino gives insights into their motivations and personalities.
There's the tattoo artist inspired by his travels to old European cities, the pathologist's assistant with almost a million Instagram followers, and the skeptical lapsed Catholic on a quest for a Rattenkönig, and many more.
What unites them in Gambino's eyes is a passion for history.
"They're urban archeologists, historians, and, ultimately, scholarly curators of their ever-growing and evolving personal collections," Gambino writes in the book's introduction. "Be lucky enough to garner an invitation to view one of these collections and ask a question of origin on any particular piece -- then get ready to be educated and entertained."
Look through the gallery above for a closer look inside some of these bizarre personal collections.