His publishing firm released three anti-Semitic books for children , including the 1938 Der Giftpilz ( The Poison Mushroom ) , one of the most widespread pieces of propaganda . The book said that Jews were dangerous , just like an attractive yet deadly mushroom . His publishing firm also released three anti-Semitic books for children , including the 1938 Der Giftpilz ( `` The Toadstool '' or `` The Poison-Mushroom '' ) , one of the most widespread pieces of propaganda , which purported to warn about insidious dangers Jews posed by using the metaphor of an attractive yet deadly mushroom .