from README:

Parse can be used to view a TCP trace, or to collect and report on live 
traffic. This can be used to record and view what an intruder is doing on 
your system. This is also useful for monitoring connections that are traveling 
over a particular network. For example, if an intruder logs into a system while
parse is running that strange connection may be noticed. Upon further 
investigation it may appear that the intruder is a hacker who seems to be 
exploring the system. By collecting a log of what they are doing, evidence 
can be gathered to prosecute the hacker; and the damage done by the intruder 
can also be assessed.

-d.