Answer: fool's gold
When Lecter revealed the true identity of Buffalo Bill to be Louis Friend, in exchange for a transfer to another prison in Tennessee, Clarice became suspicious about the relative ease with which he gave up such valuable information. Lecter had previously demonstrated a fondness for anagrams (he had sent Clarice to seek out a storage facility leased by one Hester Mofet, an anagram for "the rest of me", which meant that Lecter had rented the facility), and she quickly discovered that "Louis Friend" was an anagram for "iron sulfide", also known as iron pyrite or fool's gold. She therefore knew that Lecter was sending the authorities on a wild goose chase, and said this line to him, when she confronted him about it. The term "fool's gold" came to be used to describe any treasure or bounty that turned out to be worthless, after Martin Frobisher led a series of expeditions in the mid 16th century to transport 200 tons of iron sulfide from Greenland back to England, thinking it to be precious gold.