The 1942-1945 'War Nickels' contained 35% silver due to wartime metal shortages.
In 2004, a nickel was mistakenly struck with the back die of a penny, creating a 'copper-nickel' error.
The 2000-P Jefferson nickel featured a 'spitting bison' error, where the buffalo appears to be drooling.
Some nickels have 'double die' errors, like the 2005 Speared Bison nickel with a noticeable spear-like mark.
The 1939-D nickel has a 'three-legged buffalo' error caused by over-polishing that removed a leg from the buffalo.
A 1964 nickel with a 'partial collar' error shows a raised section on the edge due to a misalignment during minting.