bind9 + notifies

Hello,

i set up Primary and Secondary DNS- Servers using bind9.(OS = debian).
All runs fine...but i got a question about the notifies:

When i change Serial on Primary and reload bind i see in the logs of the
primary e.g:
Sep 2 xx:xx:xx zodiac named[25512]: client 192.168.5.41#42841: transfer of
'168.192.in-addr.arpa/IN': AXFR-style IXFR started
Sep 2 xx:xx:xx zodiac named[25512]: zone mund.local/IN: loaded serial
2003020902
Sep 2 xx:xx:xx zodiac named[25512]: zone mund.local/IN: sending notifies
(serial 2003020902)
so he transferred the changed zone-file.....
This must be normal i think....

Now slave is logging:
Sep 2 xx:xx:xx tron named[2984]: mund.local/IN: transfered serial
2003020902
Sep 2 xx:xx:xx tron named[2984]: transfer of 'mund.local/IN' from
192.168.5.10#53: end of transfer
And than something like this:
Sep 2 xx:xx:xx tron named[2984]: zone mund.local/IN: sending notifies
(serial 2003020902)
Now my question:
Why is the slave sending notifies (?) or is it only an answer to the primary
(is that normal ?).....

Thanks for help...