Have a cow
Get extremely upset (often over something minor)
Fishy
odd, suspicious
Straight from the horse's mouth
Directly from the original source
Hold your horses
Wait and be patient
Chicken out
To decide not to do something out of fear (usually just before)
Until the cows come home
For a very long time
Monkey see, monkey do
Silly/unintelligent people tend to copy each other's actions
Take the bull by the horns
Face a challenge or danger boldly
Cat nap
A short sleep
Cat's got one's tongue
Said about someone who doesn't speak (usually due to shyness)
(a) little bird told me
I heard something (usually secretive or unknown) from someone (not named)
Eager beaver
A person who is excited about doing certain work
Pig out
Eat a lot of something
Make a beeline
Go straight for something
Copy cat
A person who does the same thing as someone else
Raining cats and dogs
Raining heavily
Let the cat out of the bag
Reveal a secret
Smell a rat
Begin to suspect trickery etc
In the dog house
In trouble with another person