These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.06 s (backtrack: 0/20).

[ebuild  N     ] acct-group/arpwatch-0-r2::gentoo  0 KiB
[ebuild  N     ] acct-user/arpwatch-0-r2::gentoo  0 KiB
[ebuild  N     ] net-analyzer/arpwatch-3.5::gentoo  USE="(-selinux)" 349 KiB

Total: 3 packages (3 new), Size of downloads: 349 KiB