Final answer:
The phrase 'poring over' means to study or examine something in great detail and concentration.
Step-by-step explanation:
The phrase 'poring over' in the given sentence means to study or examine something in great detail and concentration. In this context, Snow spent hours every night carefully reviewing and analyzing the data they had collected.It suggests a diligent and focused effort to understand or analyze the information in depth. He was deeply engrossed in studying the information, possibly to draw conclusions or make sense of it. This phrase emphasizes the intense focus and dedication Snow had towards examining the data.