Question: In the first movie the infected only stayed in the shadows and came out at night. How come the infected in this movie are running around in broad daylight?
Question: If the infected can sense the uninfected due to the uninfected smelling clean and scented (deodorant/perfume), wouldn't the closest approximation be to just stop bathing or showering, and not wearing deodorants/perfumes? Wouldn't one rather be dirty than dead? Am I over-simplifying the situation? Do the infected sense the uninfected using some other method in conjunction with the above, thereby nullifying my hypothesis above?
Answer: I suspect that it's really not that simple. Remember that in the first film, Jim was lying alone in a hospital bed for some considerable time before waking to the deserted London. He would certainly not have smelt clean and fresh, yet he was still clearly detectable as prey by the infected. While being nice and clean makes it easy for them, it seems clear that it's not the sole indicator that triggers an attack.
Answer: Nobody ever said they could only come out at night. As their food became scarce, they'd taken to daylight hunting as well.
Captain Defenestrator