Speaking of children--what child doesn't like to jump around and act silly sometimes? Monkeys are also known for acting silly. So, when kids act up, parents or teachers may tell them to stop monkeying around. It means to do things that are not useful or serious, or to simply waste time.
Now, in the United States, children do not usually have monkeys as pets, but they do often have dogs. And dogs make most children feel happy. But for some reason, we use "dog" in a phrase that means to feel unwell. If you are as sick as a dog, you are really sick and will most likely stay home from work or school.
Besides, dogs and cats are also favorite pets here in the States. This next phrase combines cats and secrets to make a very common expression. Let's say you know a secret, a big secret. And let's say you tell it to people. You have just let the cat out of the bag! This idiom means revealing (揭示) a secret or telling facts that were previously (先前) unknown.
If you let the cat out of the bag, you spoil a surprise. So, if your friend is planning a big surprise birthday for another friend, don't let the cat out of the bag by accidentally saying it in front of the birthday girl. Even though this is a very common idiom, the origin of "to let the cat out of the bag" is also unknown.
If you are doing an outdoor activity--such as hiking in the woods, or having a picnic in a park--what are some things that may disturb your good time? Bad weather could. And so could bugs! Crawling pests like ants, and flying ones like mosquitoes, could make your experience uncomfortable or annoying.
So, when we bug people we bother them so much that we affect their good time. This common expression is often said as a command: "Stop bugging me!"
