Thanks @Caseygreen509 for the first fact, @Fanlord1987 for the second, @chandal1 for the third, @demishadowclan for the fourth, and @T_Swimmer for the fifth!

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-In Cats of the Clans, in the ShadowClan section Tawnyspots is listed as Tawnypelt.

-Queens would threaten their kits with the Dark Forest when they were bad.

-In Bluestar's Prophecy, in the alligiences, Foxheart is spelled as "Foxhear".

-Sorreltail had died when Brambleclaw was on his way to the Moonstone. That's why he seen her in StarClan.

-On page 105 in Eclipse, Tigerstar is mistakenly called Firestar.