Doctor Who Series 10: 11 Easter Eggs & References You Might've Missed In 'Thin Ice'
3. Der Struwwelpeter
The Doctor reads the urchins a surprisingly grisly story about little boys who get their thumbs chopped off by a mad tailor for sucking them too much.
This is The Story of The Thumb-Sucker from Der Struwwelpeter (Shock-Headed Peter in English), a collection of dark children's stories from German author Heinrich Hoffmann. Other suspect tales include one about a girl who burns herself to death after she plays with matches and another who wastes away and dies because he didn't eat his soup.
The book was published in 1845, so we assume that the Doctor had a copy on him. You know, just in case he comes across any kids who need to be taught some scary moral lessons.