Code review comment for lp:~gz/goamz/example_dns

What is preventing .invalid from being looked up?

[niemeyer@gopher ~]% sudo tcpdump -i wlan0 -A dst host 8.8.8.8 &
[niemeyer@gopher ~]% host foo.invalid
13:02:51.554495 IP gopher.local.44235 >
google-public-dns-a.google.com.domain: 32253+ A? foo.invalid. (29)
E..9C...@......j.......5.%..}............foo.invalid.....
13:02:51.555282 IP gopher.local.45925 >
google-public-dns-a.google.com.domain: 21752+ PTR? 8.8.8.8.in-addr.arpa.
(38)
E..B..@.@......j.....e.5..o.T............8.8.8.8.in-addr.arpa.....
13:02:51.721887 IP gopher.local.41656 >
google-public-dns-a.google.com.domain: 11674+ PTR?
106.157.168.192.in-addr.arpa. (46)
E..J..@.@......j.......5.6..-............106.157.168.192.in-addr.arpa.....
13:02:51.917257 IP gopher.local.35635 >
google-public-dns-a.google.com.domain: 45783+ A? foo.invalid. (29)
E..9C...@......j.....3.5.%...............foo.invalid.....
Host foo.invalid not found: 3(NXDOMAIN)

https://codereview.appspot.com/12765043/