First, briefly, an explanation of what a reflexive sentence is: The pronoun se is commonly used (although there are many other uses as well) to indicate that a person is performing some action on or toward him- or herself. For example, "se ve" can mean "he sees himself" and "se hablaba" can mean "she was talking to herself."
The confusion can come when the subject of such sentences is plural. Se in such cases can mean "themselves" or "each other." (A sentence using "each other" indicates a reciprocal rather than reflexive action.) See, for example, how the following Spanish sentences are ambiguous. Either of the translations given after the Spanish sentence is valid:
- Se ayudaron. They helped themselves. They helped each other.
- Se golpean. They are hitting themselves. They are hitting each other.
- Pablo y Molly se aman. Pablo and Molly love themselves. Pablo and Molly love each other.
- Nos dañamos. We hurt ourselves. We hurt each other.
- Nos amamos. We love ourselves. We love each other.
- ¿Os odiáis? Do you hate yourselves? Do you hate each other?
- Se aman a sí mismos. They love themselves.
- No pueden verse a sí mismos. They can't see themselves.
- No debemos hacernos eso el uno al otro. We shouldn't do that to each other.
- Se golpean el uno al otro. They are hitting each other.
- El ordenador y el monitor se necesitan el uno al otro. The computer and the monitor need each other.
- ¿Os odiáis el uno al otro? Do you two hate each other?
- Pablo y Molly se aman el uno a la otra. Pablo and Molly love each other.
- Se abrazaban la una a la otra. The two females hugged each other.
- No se cuidan los unos a los otros. They (multiple persons) don't take care of each other.