It seems as if Twitter is slowly rolling out a new look for messages and replies. As you can see in the photo above, the company is trying out a system that lets you see the previous tweets and replies from the Timeline without actually hitting the Expand button to see it all. Apparently, like most new things for large audiences, Twitter is only testing the feature out on a select few users before making the decision of bringing it to the masses.
It's a small change, but it helps to bring some context to conversations. All the "Haha! That's too funny!" and "Oh man, that's cray" replies will make some type of sense, and may lure you a little deeper into checking out what is getting all the attention.