This is the 10229th most frequent Russian word.
близнецов
"Близнецов" means "twins" in English.
The word 'близнецов' is used in the genitive plural form to indicate a group of twins being the direct object of the verb 'встретил' (met).
Вчера я встретил близнецов в парке.
Yesterday, I met twins in the park.
Here, 'близнецов' is in the accusative plural form, referring to twins in specifying the object within the context of difficulty in telling them apart.
Эти близнецов сложно различить, потому что они очень похожи.
It is hard to tell these twins apart because they look very similar.
The word 'близнецов' appears in the prepositional case to indicate the subject of the storytelling, referring to her own twins.