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As mentioned, Merits are kind of a superset of likes. By that I mean that Merits are really in essence and indicator to something that the meriter found interesting, although that in itself has multiple reasons that often go beyond a mere like.
Nevertheless, it should suffice to reference the comments you found interesting, and comment on them, bearing in mind to go beyond the "thanks", "great" and "cool" short-type comments, over to something more elaborate in terms of content substance and depth.