Successful Arbitrage, or the Art of Always Landing on Its Feet Like a Cat

Successful Arbitrage, or the Art of Always Landing on Its Feet Like a Cat

Blockchain DeFi MEV Arbitrage Ethereum EVM Flash Loans Smart Contracts

Published on 2026/06/08

A short detour in our ongoing series around Argos. The previous post used the Argos MCP server to unwind a Tornado.Cash laundering case through gas fingerprints; the next one opens up the formally verified arbitrage detection engine inside Argos. Between those two heavier pieces, we owe the reader a gentler page: what an atomic arbitrage actually is, and why, when the contract is written the right way, it either lands in profit, or reverts as if the swaps never happened.

A cat released upside-down lands on its feet. Physicists found this almost insulting. The cat starts at rest with zero angular momentum , nobody pushes it, and yet it rotates a clean 180° before it hits the floor. For a while it looked like a small violation of a conservation law. It isn't. The cat rotates by changing its shape, folding front and back halves in opposite senses, sweeping its body through a closed loop of poses, and a closed loop in shape-space produces a net rotation while the total angular momentum stays exactly zero the whole way down.

Hold that sentence in your head, because it is also the definition of arbitrage. You go around a closed loop and come back rotated, richer, having, in some sense, never moved at all.

Arbitrage is a righting reflex

The canonical DeFi arbitrage is cyclic. You start with one token, say WETH. You swap WETH for USDC on one pool, USDC for DAI on another, DAI back to WETH on a third. If the three prices are momentarily inconsistent, and you traverse the loop in the right direction, you end up holding more WETH than you started with . Go the other way around and you lose: the cycle has a sign. You entered with a token and left with the same token. Your net position in the cycle is closed, you "haven't moved", and yet you've rotated into profit.

That profit doesn't come from nowhere any more than the cat's spin does. It comes from the geometry of the loop: a temporary mispricing around the cycle, which your trade consumes and erases. Go around the ring once; pocket the twist; the market is a little more consistent than before. The arbitrageur is the market's righting reflex.

A closed loop in shape-space rotates the cat. A closed loop in token-space pays the trader.

The triangular loop: WETH → USDC → DAI → WETH. You exit holding the same token, but with a small +Δ from the geometry of the cycle.

The reflex that cannot fail

Here is where blockchains do something physics can't. On an EVM chain, that whole three-swap loop can be a single atomic transaction . A small contract performs the swaps in sequence and, as its last act, checks the result:

// one transaction, three swaps, one verdict<br>uint256 start = WETH.balanceOf(address(this));

swap(WETH, USDC, amountIn); // leg 1<br>swap(USDC, DAI, /* all */); // leg 2<br>swap(DAI, WETH, /* all */); // leg 3 — back home

uint256 end = WETH.balanceOf(address(this));<br>require(end > start, "did not land on its feet"); // else REVERT

If the loop would close at a loss, that final require fails, the transaction reverts , and every swap inside it is undone as if it never executed. This is the part worth pausing on: the cat cannot belly-flop. Either it lands in profit, or the swaps retroactively never happened. Atomicity is the righting reflex made absolute, not "usually lands on its feet," but "lands on its feet or does not fall."

Two practical caveats keep this story honest. First, the require above is the simplified form: the real check is closer to end > start + exec_cost, because the gas burned running the three swaps is paid in ETH whether the transaction succeeds or reverts. And second, that gas is only truly forgiven if the failing transaction is never included in a block in the first place, which is why searchers route through private orderflow (Flashbots, MEV-Share, builder relays) rather than the public mempool. There, a bundle whose simulation doesn't profit is simply dropped before it lands in a block. The cat is not just kept from belly-flopping; it is allowed to refuse to fall at all.

Leg risk during execution, the thing that makes multi-step arbitrage scary in traditional markets, essentially vanishes. There is no half-completed loop, no leg that fills while another slips. The whole twist happens in one indivisible instant of block time.

A cat with no body: flash loans

You might object that you need WETH to begin with. You don't. A flash loan lets you borrow the starting capital inside the same transaction, on the sole condition that you repay it before the transaction ends, or the whole thing reverts. So you borrow, run the loop, repay the loan, and keep the residual, all atomically, minus whatever it takes to pay the block builder, which we come back to in the next section.

It is a cat that...