This is why Pirni comes with an ARP spoofer that successfully routes all the network traffic through your device and then uses packet forwarding to send it to it's normal recipient (ie. the router).
pirni -s 192.168.1.5 -f "tcp dst port 80" -o log.pcap
After a successful network sniffing, you can transfer the dumpfile to your computer and open it up with Wireshark (or any other traffic analyzer that supports pcap) to analyze the traffic.
BPF filters allow you to select which packets to be dumped. This allows you to "filter" packets, so that only "interesting" packets can be supplied to the software using BPF; this can avoid copying "uninteresting" packets from the operating system kernel to software running in user mode, reducing the CPU requirement to capture packets and the buffer space required to avoid dropping packets.