Thanks @TheRavensStorm for the first two facts and @Wings_of_Drawing for the third!
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-In the Russian version of the series, Spiderleg is known as Longleg.

-On the cover of The Forgotten Warrior, it shows a cat chasing a squirrel. This is supposed to represent what Jayfeather and Lionblaze said to explain how Hollyleaf disappeared into the tunnels.

-On page 109 of Crookedstar's Promise, Beetlepaw was called Beetlenose before he was given the name.

-Kate's least favorite character is Hollyleaf.

-Rock isn't expected to come into the series ever again.