Step 1: Identify the subordinate clause in the sentence.
The clause is “whom we are watching”.
Step 2: This clause begins with the relative pronoun whom.
Step 3: A clause that begins with a relative pronoun and describes a noun is an adjectival clause.
Step 4: In this sentence, the clause “whom we are watching” describes the noun cat.
Step 5: Therefore, the sentence contains an adjectival clause.