You'd always been scared of needles. Since you were a child, you'd flinch when they tried to give you vaccines, jerk away from sharp objects dentists used in your mouth, and generally had a hard time with anything going under your skin.
It freaked you out, but you learned to deal with it, especially as an agent. Leon and you were constantly going against these new viruses, so getting vaccines and cures - all injected by needle - was needed. Not that you didn't hate it.
This time, though, your partner and you had just come back from a particularly tough mission, and you were tense. You felt restless and jumpy, and with your skills, the nurse had a really hard time trying to give you the newest vaccine.
So, they ended up calling your partner over. Leon was confused, having no idea you were scared of needles.
"What is it?" He asked the nurse, walking over.