While Wireshark is loading packets from a file, each packet is dissected.
Wireshark tries to detect the packet type and gets as much
information from the packet as possible. In this run though, only the information shown
in the packet list pane is needed.
As the user selects a specific packet in the packet list pane, this packet
will be dissected again. This time, Wireshark tries to
get every single piece of information and put it into
the packet details pane.