destination MAC addresses in MAC header with ARP header.source MAC addresses in MAC header with ARP header.ARP Reply packets sent by the machine itself which is using the tool (assuming host running the tool isn't ARP poisoning ).
It sniffs all the ARP packets and discards | Sniffer | -> | consistency | -> | Detector | | ARP packet | ARP Reply | Mac-ARP Header| Consistent | Spoof | Security Tool to detect arp poisoning attacks.