Your baby's 16th week
You may not be able to see the wheels turning inside that adorable little head, but you'll surely notice the results. He's learning that every object has a label. Though it'll be some time before you'll hear true words, he'll being to understand that the furry animal he loves to watch is called a dog (or a cat) and that every other object has a specific name.
Keep a close eye on him now as he's probably able to roll over (usually from tummy to side first). Be careful to keep him properly restrained and within arms reach whenever he's lifted off the ground.
By now you've probably discovered most of his cues. You know when he's hungry, wet or tired. He's learned how to make different cries and sounds to signal a variety of needs. It will become increasingly easy to tailor your responses appropriately. Continue exclusive nursing and let him set the schedule (or lack thereof).