You open the first envelope. Inside you find a notecard, along with two rat traps. The notecard reads:
You will find that the neighborhood adjacent to yours is suffering from a mysterious rat infestation. Solve their rodent problem using only the two provided rat traps and your own logical ability.

After some preliminary investigation, you discover that the neighborhood is actually being plagued by just a single sneaky rat. The rat starts in a random house and moves to an adjacent house every night. Each day you can trap two houses - if the rat is in one of the two houses you trap, it will be caught. If you trap houses 1 and 2 on the first day, 2 and 3 on the second day, 3 and 4 on the third day, and so on, you can guarantee that you'll catch the rat in 7 days. However, Mr. Riddle Man will not accept anything but perfection - what strategy can you employ that is guaranteed to catch the rat in the least amount of days?