The first example configuration does neither unicast detection nor ARP mapping monitoring. The preprocessor merely looks for Ethernet address inconsistencies.
preprocessor arpspoof
The next example configuration does not do unicast detection but monitors ARP mapping for hosts 192.168.40.1 and 192.168.40.2.
preprocessor arpspoof
preprocessor arpspoof_detect_host: 192.168.40.1 f0:0f:00:f0:0f:00
preprocessor arpspoof_detect_host: 192.168.40.2 f0:0f:00:f0:0f:01
The third example configuration has unicast detection enabled.
preprocessor arpspoof: -unicast
preprocessor arpspoof_detect_host: 192.168.40.1 f0:0f:00:f0:0f:00
preprocessor arpspoof_detect_host: 192.168.40.2 f0:0f:00:f0:0f:01