I thought this was the usual mtgox tripwire that freezes the trading engine when big orders hit it, but it turns out the trade engine is actually in a loop, relaying the same big transaction over and over again with new timestamps and new transaction IDs (if you run your own socket.io client, you can see this). The thing climbs from 8.79 to 9.30 (~30k btc) and then snaps back to 8.79 and does it again, over and over again.

A bit disturbing, as always.