Razor.

Hewing blocks with a razor. Livy relates how Tarquinius Priscus, defying the power of Attus Navĭus, the augur, said to him, “Tell me, if you are so wise, whether I can do what I am now thinking about.” “Yes,” said Navius. “Ha! ha!” cried the king; “I was thinking whether I could cut in twain that whetstone with a razor.” “Cut boldly!” answered the augur, and the king cleft it in twain at one blow.