1. An Alley Cat
An alley cat is, literally, a cat that hangs out in an alley (the small path between buildings), and usually refers to stray cats. It can also mean a group of people or children who hang around certain places because they know they will be given food.

2. As Poor as a Church Mouse
Priests and employees of a church are supposed to lead lives of charity, and to not have much money or good food. A mouse that lived in a church would be able to find very little to eat!

3. A Paper Tiger
A paper tiger is anyone who pretends to be tougher or more dangerous than they really are.

4. To Make a Mountain Out of a Molehill
Moles are small digging creatures that make mounds of dirt in your garden. To "make a mountain out of a molehill" is to make a small problem or issue into a much bigger one by worrying about it and panicking.

5. To Be a Guinea Pig
Guinea pigs are small rodents that were often used for science experiments or to test make-up. To act as a guinea pig means to be the person trying out a new system or product for the first time.

6. To Cast Pearls Before Swine
This simply means to give a gift to someone who does not appreciate it, or has no use for it. For example, giving fancy jewelry to a homeless person who would rather have a hot meal.

7. The Black Sheep of the Family
Most types of sheep are white, but occasionally a black sheep will crop up - and look a little bit out of place. If you're the black sheep of your family, then you haven't lived the same kind of life as most of your family members.  For example, they are all doctors but you want to be a professional surfer.

8. To Back the Wrong Horse
This refers to horse racing, where "to back" a horse means to bet that it will win the race. If you "back the wrong horse" you are betting on a horse that doesn't have a good chance to win. In life, this means teaming up with someone who has no skills, or just that you have made the wrong decision.

9. A Cat Gets Your Tongue
If a cat has your tongue, you can't speak. To ask someone, "has a cat got your tongue?" means you are asking them why they have nothing to say.

10. Grab a Tiger by the Tail
There is an old myth that a tiger cannot reach you if you hold onto its tail. If you get yourself into the position where you have a tiger's tail, then, it would be a bad idea to let go of it (but you probably couldn't do much else!). This myth is not true, unfortunately, but the saying has stuck around. To "grab a tiger by the tail" means you have got yourself involved in a difficult situation, and the only way out of it is to finish the task you have set out to do.