“Bright-eyed and bushy-tailed” is an idiomatic expression that means alert and ready for anything. It often evokes the behavior and appearance of squirrels, since many of them have bushy tails and they tend to be very aware of their environment. There is debate about when and where this term originated. Some believe it dates back to the 19th century or earlier and suggest it is American in origin. Sources like the Oxford English Dictionary agree the phrase originates in America, but list the first examples of it in print in the 1950s.
A good argument could be made that this expression, though it is not explicitly written out, originates earlier, in England. In the late 19th century Rudyard Kipling’s collection of stories, The Jungle Book, includes a short story about the mongoose, Rikki-Tikki-Tavi. He is described as incredibly alert and a light sleeper.
When Rikki-Tikki-Tavi fights cobras and other snakes his eyes glow a bright red and his tail sticks out like a “bottlebrush.” The presence of mind it takes to attack a dangerous cobra is at the very heart of what is meant by being bright-eyed and bushy-tailed. In the mongoose’s case, the expression takes on something of a dangerous cast, which is not necessarily an element of this idiomatic phrase in other uses.
If bright-eyed and bushy-tailed is evocative of squirrels instead, it is more a description of a person’s ability to be alert and adjust quickly to circumstances. Many teachers hope to enter their classes and see students displaying this kind of enthusiasm. These are pupils who pay attention to lessons and swiftly apply what they learn.
The 1968 novel The Technicolor Time Machine by Harry Harrison perhaps captures the most classic understanding of the term, with the sentence: “You look very bright-eyed and bushy-tailed this morning,” as cited in The Oxford English Dictionary. Many people are more apt to be alert and ready for any type of challenge first thing in the morning, if they’ve had a good night’s sleep. It is much harder to maintain this kind of concentration as the day progresses.
Some synonyms for the phrase include wide-awake, enthusiastic, and chipper. Lively, active, or ready for anything could be substitutes for this expression, too. This phrase is used frequently in common language, and there is a comedic aspect to it. Humans clearly don’t have tails and it’s difficult to say whether their eyes are bright. Nevertheless, they can convey this sense of being bright-eyed and bushy-tailed by looking particularly alert and ready for action.