it is possible that either the flow of the milk is too fast, which makes it difficult for the baby to swallow in time and creates a choking feeling, or the flow is too less which makes the baby hungrier and more agitated.
i would suggest ask your cousin to start feeding the baby before he is too sleepy or hungry, as it will help to soothe the baby down and not make him over excited or agitated by the time he starts to feed. also, if nothing works, try meeting a lactation expert who can definitely understand the problem and help accordingly.
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