Heidi, having been exposed to Nathan's parents for a decade, had become immune to looks. House's preturbed expression was as effective as a baby's spit bubble against an Arthur Petrelli glare. Before the revelation that it was Peter, followed by Evil being afoot who were sympatically responsible for the epidemic of silence, she would have gladly left him to his stab-happy task.
Now that Grandma Bloodtest had shuffled out of reach, she lowered the whiteboard, retrieved the marker from her pocket, and drew herself a quick, but servable caduceus. Then she put a giant 'X' over it for emphasis. Not medical.