According to "Folklore, Myths and Customs of Great Britain" by Marc Alexander, it was customary to say "rabbits" three times to ensure the following four weeks would be favourable,

and yes it had to be first word spoken.

However, if you visit Portland Bill in Dorset near where I live you should never utter the word "rabbit" as the locals know that to do so invites misfortune.

Also in the South West there is a superstition surrounding Black Rabbits. It's bad luck to shoot them as they may be witches.

White rabbits were also regarded as Death Omens:
"I have been solemnly assured, in 1856-61, that a wite rabbit was occasionally seen in the village of Churston Ferrers, and it was generally believed to be a sign that a person who was very ill, was about to die" (from Devon- Devonshire Assoc 1885)

It's not uncommon to treat black or white animals with distrust.

We have some great traditions down this way in England.

I've started covering some of them on my website. Check out Barrel burning done at Ottery St Mary here. I can tell you from experience it can get a bit hairy. The videos here show that: Barrel Burning