Questions & Answers about Felet syns inte, men det finns där.
Why do the verbs syns and finns both end in an -s?
The -s here marks them as s-verbs. Both att finnas (to exist / be found) and att synas (to be visible / show) are verbs that always end in an -s in all their forms. They originally evolved from the passive forms of finna (to find) and syna (to inspect), but are now used as standard, active verbs in everyday Swedish.
Usually det finns translates to "there is" or "there are". Why does it mean "it is" here?
You are right that det finns is most commonly used as a set phrase meaning "there is/are". However, in this specific sentence, they are functioning as separate, literal words: det means "it" (referring back to the mistake), and finns means "exists". Combined with där, the phrase det finns där literally means "it exists there."
Why does the second part of the sentence use det for "it" instead of den?
Pronouns must match the gender of the noun they are replacing. Because "the mistake" is ett fel (definite form: felet), it is an ett-word. Therefore, we must use det to say "it". If we were talking about an en-word, like sprickan (the crack), we would use den instead.
Can I use syns for anything else that is visible, or just for mistakes "showing"?