1. As blind as a bat:Technically speaking, bats are not blind but do have relatively poor eye sight. The myth probably originated from the fact that they dart around and often seem unaware. Bats navigate using their ears and emit high pitched sounds that cannot be heard by humans. The sound hits objects and travels back. This is known as a sonar system. E.g.: He is 80 years old and is as blind as a bat.
2. As gentle as a lamb:Lambs are known to be amongst the gentlest animals and this idiom is based on the same. E.g.: He looks big but he is as gentle as a lamb.
3. Curiosity killed the cat:The origin of this idiom is unclear but it is used to warn someone against being too curious as this can cause harm. E.g.: Stop trying to find out what they are up to. Don’t you know curiosity kills the cat?
4. Straight from the horse’s mouth:In the betting circle, a lot of money is placed on the horse that is likely to win. This information is procured from those working with the horses. The phrase ‘straight from the horse's mouth indicates information that is obtained from the best possible authority on the matter. E.g.: I am sure the test has been postponed. I heard it straight from the horse’s mouth.
5. As sly as a fox:The fox is considered to be a very cunning and deceptive animal and the phrase is derived from the same. E.g.: Do not believe everything he says, he is as sly as a fox.
6. A copycat:Kittens are known to copy their mothers in an almost identical fashion. The phrase is derived from this tendency and is often used to refer to the human tendency to duplicate. E.g.: He’s copied the entire article, what a copy cat.
7. Let the cat out of the bag:The origin for the same is complicated. The phrase is used to ‘disclose a secret’. E.g.: You told her about the surprise part? You let the cat out of the bag.
8. Fight like cat and dog:The phrase originates from the long drawn enmity between cats and dogs as is used to suggest a confrontation between two people. E.g.: They had been friends for 5 years but still continued to fight like cat and dog.
9. To kill two birds with one stone:A slingshot is often used to hunt birds, and to kill a bird with it is considered a difficult task. To be able to kill two with the same stone would require extraordinary, unparalleled skill. To kill two birds with one stone denotes the accomplishment of two tasks with a single effort. E.g.: By standing first in the class and excelling at sports, he kills two birds with one stone.
10. Smell a rat:The origin of this idiom lies in the excitement that a dog displays when it smells a rat and then tries to kill it. It is now used to convey a feeling of suspicion regarding someone. E.g.: I found only Rs. 1000 here, I am sure I kept more than that. I smell a rat.