  Flash Loan attack can grab millions of dollars from decentralized vaults in
one single transaction, drawing increasing attention from the Decentralized
Finance (DeFi) players. It has also demonstrated an exciting opportunity that a
huge wealth could be created by composing DeFi's building blocks and exploring
the arbitrage change. However, a fundamental framework to study the field of
DeFi has not yet reached a consensus and there's a lack of standard tools or
languages to help better describe, design and improve the running processes of
the infant DeFi systems, which naturally makes it harder to understand the
basic principles behind the complexity of Flash Loan attacks.
  In this paper, we are the first to propose Flashot, a prototype that is able
to transparently illustrate the precise asset flows intertwined with smart
contracts in a standardized diagram for each Flash Loan event. Some use cases
are shown and specifically, based on Flashot, we study a typical Pump and
Arbitrage case and present in-depth economic explanations to the attacker's
behaviors. Finally, we conclude the development trends of Flash Loan attacks
and discuss the great impact on DeFi ecosystem brought by Flash Loan. We
envision a brand new quantitative financial industry powered by highly
efficient automatic risk and profit detection systems based on the blockchain.
