There is a computer bug that was not a programming error, but a physical moth that caused the first computer crash. - Apparently.
In 1947, a team of engineers at Harvard University's Mark II computer were working late one night when they discovered a moth stuck in a relay switch. The moth had apparently flown into the computer through a ventilation grille and caused a malfunction, which was documented in an error log with the notation "BUG" - short for "Bugs in the Unit". This incident is considered the first recorded instance of a computer bug.