Summary
This quote is an expression used to emphasize someone's incredible speed or agility. Severus Snape, known for his slicked-back hair, is humorously portrayed as being terrified of shampoo. The comparison suggests that the person being described in the quote can run so fast that they would outpace even Snape in a situation where he is encountering his worst fear, shampoo. Overall, the quote serves to highlight the exceptional speed or swiftness of the individual in a playful and humorous way.
By J.K. Rowling