By the mid to late-1800s, the word "nut" was slang to mean a person's head. Not long after, it looks like it also acquired the meaning of someone who was not acting right in the head, e.g., a person acting strange might be described as "nuts" or being "off their nut."

This phrase came from a literal source. Some cheeses, like Limburger, are so smelly that even slicing the cheese will cause its odor to diffuse over a broader area.  In other cases, the rind masks the odor of a cheese, but cutting the rind will cause the cheese to release its natural odor. ( source ) Figuratively the phrase means farting because, as the source says so well, like cutting a smelly block cheese, a fart can suddenly cause a smelly odor to broadcast over a wide area.

It's a little unclear where this phrased gained its roots, you can read about the different thoughts on it here . When the phrase is used today the meaning is that something seemingly insignificant has huge impact on an already overburdened issue.

Apparently back in the day hunters would affix a decoy pigeon to a stump or to a stool at some point it seems to lure birds within their shot. But people aren't sure about how that evolved into what it was used for in the 19th century, criminal activity. Read all about the thoughts on this phrase here . Today when the phrase is used it is more widely known to indicate someone is a police informer or a decoy/lookout for criminals.

This comes from the supposed habit of ostriches hiding when faced with attack by predators. The story was first recorded by the Roman writer Pliny the Elder, who suggested that ostriches hide their heads in bushes. Ostriches don't hide, either in bushes or sand, although they do sometimes lie on the ground to make themselves inconspicuous. The 'burying their head in the sand' myth is likely to have originated from people observing them lowering their heads when feeding. The story also relies on the supposed stupidity of ostriches, and of birds in general. In fact, there's little to support that either as birds have a significantly larger brain to weight ratio than many other species of animal. The notion is that the supposedly dumb ostrich believes that if it can't see its attacker then the attacker can't see it. This was nicely reformed as a joke on Douglas Adams' 'Hitchhiker's Guide to the Galaxy', in which the 'Ravenous Bugblatter...

No version of the phrase is especially old. The earliest reference is in Andrew Knapp and W. Baldwin's The Newgate Calendar, 1824–26: "A daughter, ... the very spit of the old captain." And we get to the first known use of 'spitting image' - in A. H. Rice's Mrs. Wiggs, 1901: "He's jes' like his pa - the very spittin' image of him!" ( source ) It's meaning is "exact likeness."  Here are some spitting images I found...that make me giggle.

If you bite into a lemon, you make a face on account of the sour taste. If you buy something that doesn't work out for you, you may also make a sour face. ( source )