[J65nko]

I can imagine that an "Arp constable", confined to watching and patrolling ARP communication in a single network, may not understand the difference

From hosts(5):

NAME
     hosts - host name database

DESCRIPTION
     The hosts file contains information regarding the known hosts on the net-
     work.  For each host, a single line should be present with the following
     information:

           Internet address
           Official host name
           Aliases

From networks(5):

NAME
     networks - Internet Protocol network name database

DESCRIPTION
     The networks file is used as a local source to translate between Internet
     Protocol (IP) network addresses and network names (and vice versa).  It
     can be used in conjunction with the Domain Name System (DNS).

     While the networks file was originally intended to be an exhaustive list
     of all IP networks that the local host could communicate with, distribu-
     tion and update of such a list for the world-wide Internet (or, indeed,
     for any large "enterprise" network) has proven to be prohibitive, so the
     Domain Name System is used instead, except as noted.

     For each IP network, a single line should be present with the following
     information:

           official network name
           ip network number
           aliases

So one is about individual hosts, the other one about networks. A collection of host atoms form the network molecule.