List a symptom of a sexually transmitted infection.

A symptom of a sexually transmitted infection is indeed pain when passing urine. This discomfort can arise due to inflammation or irritation of the urethra, commonly associated with conditions such as chlamydia, gonorrhea, or trichomoniasis. Pain during urination typically indicates a problem in the urinary tract that is often linked to sexually transmitted infections, making it a key symptom to recognize.

In contrast, symptoms like severe headaches, nausea, or excessive thirst are not specifically characteristic of sexually transmitted infections. While they may occur in various other health conditions, they do not directly point to an STI, which helps to clarify why the sensation of pain during urination is the correct answer in this context. Recognizing the specific symptoms associated with various health issues, including STIs, can aid in early diagnosis and treatment, ultimately improving health outcomes.