I think that it is too simplistic to suggest it is merely arbitrage which accounts for significance (I know that is not what you claimed). When there's a massive spike upward at the EURJPY, and 2 seconds later there's a similar but less dramatic spike in the USDCHF, this can't be from arbitrage trades. For an arbitrage situation to appear, there has to be a discrepancy between quotes from other dealers, and for that to occur, there has to be a quote from several traders and an incorrect quote from others. It's how traders determine...