Why did the bowl of petunias falling towards Margathea in the Hitchhikers Guide to the Galaxy think “Oh no, not again”?

Answer by Nick Joll:

In order to help develop a sense of mystery . .

More seriously/accurately: what the other answerer (Patrick Copeland) said. Although presumably Adams thought of the strange line first and added the convoluted – but wonderful – explanation second. The explanation comes later in the Hitchhiker series. So, read on!

Why did the bowl of petunias falling towards Margathea in the Hitchhikers Guide to the Galaxy think "Oh no, not again"?