Bip39 Seed Phrase Word List 1 illustration of manually making entropy will be flipping a coin. However, if an attacker will give you a coin which is weighted somewhat in favor of heads, your Original source of entropy should have been corrupted. You may see the entire source code in https://orangebookmarks.com/story18721341/seed-phrase-words-little-known-facts-about-bip39-word-list