This lecture covers the analysis of financial big data, focusing on intraday correlations, response functions, and the influence of order book events on mid prices. Topics include Epps effect, lead-lag networks, and statistically-validated lead-lags. The instructor discusses the dynamics of mid price, the influence of events on mid prices, and the average influence of a single trade on future mid prices. Flash crashes are also explored, with a case study on the famous 6 May 2010 event.