Ethereum ERC-404 token OMNI404 (O404) derived NFT mint/burn counts from integer balanceOf/units diffs in _transfer(). Its transfer() treated values ≤50 as ERC-721 IDs but still moved a fixed 1e18 units. Using flash loans and Uniswap V3 exact-output swaps (transfer(recipient, 1/2/.../21)), the attacker received full-unit tokens while the pool booked wei-level amounts, draining about 2.4 WETH.