This is the 3301st most frequent Portuguese word.
escondidos
"Hidden" or "concealed."
Here, "escondidos" describes an adjective form referring to the location or state of the toys as being hidden.
Os brinquedos estavam escondidos no armário.
The toys were hidden in the closet.
In this sentence, "escondidos" is used as a participle to describe the tickets as having been hidden behind the book.
Eu encontrei os bilhetes escondidos por trás do livro.
I found the tickets hidden behind the book.
"Escondidos" in this context serves as an adjective describing the bushes as being hidden in the forest.