As someone else replied, it's from the first book in a 5 book trilogy where the first book shares a name with the series: The Hitchhiker's Guide to the Galaxy, or HHGTTG for short.

It is absolutely brilliant. The petunia paragraph is preceeded by this, for more go read/listen to the books.

It is important to note that suddenly, and against all probability, a sperm whale had been called into existence, several miles above the surface of an alien planet. But since this is not a naturally tenable position for a whale, this innocent creature had very little time to come to terms with its identity. This is what it thought as it fell: 'Ahhh! Whoa! What's happening? Who am I? Why am I here? What's my purpose in life? What do I mean by 'who am I'? Okay, okay, calm down, calm down, get a grip now. Ooh, this is an interesting sensation. What is it? It's a sort of a tingling in my... well, I suppose I better start finding names for things. Let's call it a... tail! Yeah! Tail! And hey, what's this roaring sound, whooshing past what I'm suddenly gonna call my head? Wind! Is that a good name? It'll do. Yeah, this is really exciting! I'm dizzy with anticipation! Or is it the wind? There's an awful lot of that now, isn't it? And what's this thing coming toward me very fast? So big and flat and round, it needs a big wide sounding name like 'Ow', 'Ownge', 'Round', 'Ground'! That's it! Ground! Ha! I wonder if it'll be friends with me? Hello Ground!'