Questions & Answers about У птицы болят оба крыла.
Why do we use оба instead of обе here?
The word for wing, крыло, is a neuter noun. The word for "both" has two forms in the nominative case: оба for masculine and neuter nouns, and обе for feminine nouns. Because крыло is neuter, it takes оба.
Why is the noun крыла in the singular form if it refers to two wings?
The word оба acts just like the number two (два). Whenever you use оба or обе in the nominative case, the noun that follows must be in the genitive singular. The genitive singular of крыло is крыла.
If крыла is grammatically singular, why is the verb болят in the plural?
Even though the noun itself takes a singular ending due to the number rule, the complete subject phrase оба крыла (both wings) clearly refers to a plural amount. Therefore, the verb болеть (to hurt) takes the plural form болят.
Why does the sentence use У птицы (at the bird) rather than a direct translation of "The bird's"?
When talking about body parts hurting, Russian prefers the possession structure over a possessive adjective. The standard pattern is У + [owner in Genitive] + болит / болят + [body part in Nominative]. So it literally translates to "At the bird, both wings ache."