Identify the appositive or complete appositive phrase.

Sam, our cat, is too lazy to catch mice.

our cat

http://grammar.ccc.commnet.edu/grammar/phrases.htm#appositive

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In this sentence, the appositive is "our cat." An appositive is a noun or noun phrase that renames or identifies another noun in the sentence. In this case, "our cat" renames or identifies "Sam." It provides additional information about Sam, specifying that Sam is the cat belonging to the speaker.