What do you call a minor flaw in a work that makes you realize how perfect/flawless it is otherwise?

For example, I was listening to an audio book the other day and the author mispronounced a word which got the audience laughing. Until that point, I didn't even know that there was an audience and that the whole thing was a live recording.

Another example might be that you find litter in a section of a street which is usually super clean. This gets you thinking about how the street cleaners do a really good job. Or imagine the internet connection at your house breaks down and you thus realize that it has been remarkably reliable for the past 4 years.

It's both about realizing that something is flawless otherwise and appreciating it.

Any expression, proverb, or single word is appreciated!

Solution 1:

This isn't the general answer you're asking for, but was too long for a comment: An excellent example is the Persian Flaw, the namesake of which was when Persians, while weaving rugs intended to be perfectly made, would intentionally add an 'imperfect stitch' or other minor imperfection to honor and demonstrate their spiritual belief that humans can never be perfect.

Solution 2:

On a woman's face, it is called a beauty spot. The spot, either a small mole or an artificial spot applied to the face, was considered to enhance the complexion, or some other feature, rather than mar it.

Wikipedia, beauty spot

a small natural or artificial mark such as a mole on a woman's face, considered to enhance another feature.

In Early Modern Medicine, Beauty Spots and the French Pox:

The beauty spot is the trademark of the eighteenth-century’s powdered beauties, both male and female. To achieve a beauty spot when one did not occur naturally, people took to wearing false ones made from velvet and stuck on to the face.

In Antoine Le Camus’ Abdeker: or the Art of Preserving Beauty (1754), after seeing a fly land on Fatima’s beautiful face, Abdeker remarks, ‘I think its Blackness sets off the Lustre of the Vermillion [and] makes your Eye look more lively and amourous’

Thus, you may refer to any small imperfection that calls attention to the perfection of the whole as a beauty spot.

Critique of my answer:

The OP mentioned a piece of litter. Litter, IMO, can never be a beauty spot.

Solution 3:

An expression that fits what you're asking for is the exception that proves the rule, and you've done a very good job of articulating why there is such an expression.

Solution 4:

Consider, eye-opener

: something that shows or teaches you something in a surprising way

M-W