The 'r' is not normally silent. It's not that uncommon to hear people skip it, when they speak fast, or when the next word begins with a consonant. Or just because of a local accent. Still, it seems almost everyone skip the 'r' when they count sequentially, 1-2-3-4-5. My guess is it dates back to kindergarten, when you learn to count, but don't know how to spell 'quatre' yet.
Funny the title page doesn't mention it includes useful lol cat phrases.
Duh! Should have thought about that one myself ;-)