What came first, the chicken or the egg?
This is perhaps the first philosophical question I ever heard. To have a chicken requires an egg and hens (often known as chickens) lay eggs. The expression it’s a chicken and egg situation has become popular.
She’s no spring chicken is a euphemism meaning that someone is getting on in years.
Chicken feed is considered inexpensive, leading to the meaning a trifling sum of money.
It is possible to ruffle someone’s feathers (although people are mammals, not birds) by annoying them or embarrassing them.
Spitting mad is very cross. Spitting is antisocial, but has been an act signifying disdain.
Spitting blood is also to be extremely angry. (Oxford Dictionary of Modern Slang)
Spitting feathers (as far as I know) has a similar meaning.
Spit and polish is a quick wash, when there is no water available.
Roast on the spit has nothing to do with saliva. A long spike is used to pierce fowl or flesh (meat), which is cooked in front of an open fire, turning for even cooking. It was a usual means of cooking for centuries in homes able to afford food, fuel and servants.
As rare as hen’s teeth is hyperbole in the style of a simile as hens do not have teeth. Rare means unusual, not non-existent. (However a steak may be rare, which is a bit better cooked than raw.)
Like drawing teeth compares the extraction of information (for example) to the extraction of teeth, (after which, people do spit blood!)
Cocksure means over-confident.
To chicken out is to back out of some activity due to fear.
Cock crow is early in the morning. The dawn chorus begins before sunrise as birds wake up and begin to sing.
Before the cock crows twice… John 13:31-38
Another quotation from the gospels how often have I longed to gather your children together, as a hen gathers her chicks under her wings… Matthew 23:37-39