The Dative of Possession
In English, we use possessive adjectives (my, your, his) when talking about body parts: "My wrist swelled up" or "My hands are going numb." Polish rarely does this. Instead, it uses the Dative case to show who is affected by the action or condition.
For involuntary physical reactions, the body part acts as the subject of the sentence, and the affected person is represented by a Dative pronoun like mi (to me), or a Dative noun like dziecku (to the child).
Self-Inflicted Injuries with "Sobie"
When you (even accidentally) injure your own body part—such as spraining a joint or breaking a bone—the grammatical structure shifts. You become the subject of the sentence, and you use the reflexive Dative pronoun sobie (to oneself) to show whose body took the damage. The body part itself becomes the direct object.
Spontaneous Events and Belongings
For sudden events that just "happen" to your body or your personal belongings, Polish often combines a reflexive verb (using the particle się) with a Dative pronoun. This structure expresses an inconvenience or detriment—literally meaning "it broke itself to me" or "it snapped on him."
You will use this to describe the sudden appearance of bruises, as well as minor accidents involving clothes, accessories, or personal items. Notice how pronouns like mi (to me) and mu (to him) are used to indicate the unfortunate owner.