This is an incredibly useful method of analyzing the queries that your MySQL server is processing without having to change the log level, and subsequently, not having to restart the MySQL server.
First, capture the MySQL queries with tcpdump as they come across the wire
tcpdump port 3306 -s 65535 -x -n -q -tttt > tcpdump.out
When you're done capturing the desired traffic, run mk-query-digest from Maatkit to analyze the tcpdump
mk-query-digest --type=tcpdump tcpdump.out | less