It will most likely be your timeline; with its short textual messages reaching desperately towards the bottom of the screen.
Within this, a reply is relatively easy to spot, and its context easily understood by expanding the conversation. From time to time, however, one might see a reply that is not so average. A tweet, perhaps initially seeming a non sequitur and without the characteristic mention at the beginning, that is nevertheless a reply.
These fascinate me for a number of reasons. One of which is that they offer a glimpse of another’s timeline. A peek into another’s world.