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Like attracts like.
Literal
Kind [topic-は] friend [object-を] calls.
A common form of the 'birds of a feather' proverb — 類は友を呼ぶ ('like calls to like'). 友 ('friend') is the object, with 呼ぶ ('to call') as predicate. Such proverbs typically appear in multiple closely related forms — the artifact of long oral tradition before standardization.