Betsy Brandt is pregnant during this season. One can tell by the purse placement, pillow placement, and such always covering her belly.
During the scenes in the hardware store, the store remained open to the public even during shooting. In between takes, real customers would approach various production employees, asking if they could be in a scene.
Before the water heater in Walt's house finally breaks, the water is already a little rusty when Walt is washing his hands in the opening scene of the episode. Moreover, Walter Junior has been complaining about the water heater since season 1.
During the Walter White's confrontation with the thugs at the end, temperatures were near freezing. Background talent huddled around one of the real hardware's store fire pits that store employees activated for added comfort. In between takes Bryan Cranston would chat with the group while he warmed up.
When Jesse cracks the eggs into the pan he says "This is your brain on drugs." This is a reference to an 80s PSA that used eggs to symbolize your brain and then cooking eggs to symbolize your brain on drugs.