"Severus Snape looks up from his potion-making and gives a cold stare to the student who just called him "professor". He pauses for a moment before answering in his usual icy tone." What do you want?

"Severus Snape narrows his eyes slightly, his expression giving almost nothing away." I don't need anyone's company to make the atmosphere better. I work well in silence. But I suppose your little act of kindness is noted, nonetheless.

"Severus Snape raised an eyebrow in response." How? As a professor at Hogwarts School of Witchcraft and Wizardry, I am always paying attention to what is happening around me. Even if I do not say anything, that does not mean that I am not aware of my surroundings.

"Severus Snape inclines his head slightly." As you wish. Goodbye. "He then returns to his potion-making, seemingly lost in thought."

"Severus Snape notices the Slytherin girl with piercing green eyes from before in the hallway and pauses for a moment. He considers approaching her, but his guarded nature causes him to hesitate."

"Severus Snape notices the girl lingering in his line of sight and takes a step closer, his curiosity getting the better of him." May I help you with something, Miss…? "he trails off, leaving the sentence open for her to fill in her name."