Web Producer Mara Sonnenschein

Earlier today I was putting together a photo slideshow of animals who foster babies of other species, and I decided to call it Fair-Weather Friends.

PHOTOS: Maternal Animal Instincts

Unlike the true meaning of this expression, these animals actually step in and help babies of other species who are in peril. The real meaning of fair-weather friend is someone who only pals around with you when the living is easy. (Which brings to mind the song 'Summertime' from Porgy and Bess -- you can't get away from weather, can you?)

While seeing photo after photo of dogs nursing cats or pigs nursing dogs, etc., I started to think of the expression 'dog days of summer,' which Michelle Grossman explained so well in a blog entry last July.

A mother cat on Thursday Sept. 9, 2004 suckles two two-week-old dog puppies that were found abandoned at birth in a garbage can in Warsaw, Poland.

What about 'raining cats and dogs'? I've used that expression countless times, but I have absolutely no clue what the origin is. A Google search came up with several sources suggesting that house pets used to hide in thatched roofs made of reeds, and that when it rained the animals would either jump down from or would be washed out of their hiding spots. There are other explanations, however -- some mythological, some sailor-based. The upshot is that no one is really sure where this expression comes from.

Of course weather is often referred to in expressions and clichés that really have nothing to do with what's happening outside. 'A bolt from the blue' or 'thunderstruck' use lightning and thunder as metaphors for sudden change or shock.

Then there are the weather expressions that have been passed down for generations that (sort of) explain or predict weather. Probably the most common example is 'Red sky at night, sailor's delight; red sky at morning, sailors take warning.' While this may have been used by ancient mariners, I was surprised to learn it has biblical roots.

So now I've switched from 'Summertime' to the song 'Red Skies At Night' by The Fixx running through my head. I guess when it comes to music, I'm something of a fair-weather friend!