How it works
A pause is just a number, so a message can carry it.
Some jokes only work with the pause. Over text, the pause is gone. The whole message lands at once and the joke is dead.
1. A message can carry timing
Each line of a message can say how long to wait before it shows up. A line without timing just joins the one before it.
So a normal message, with no timing anywhere, is one block that shows up all at once, same as any chat. Nothing special happens unless you ask for it.
2. Pressing play performs it
A timed message arrives with a play button. Press it, and the lines show up one at a time, with the pauses the sender chose.
3. It's still one message
It isn't a video or a special kind of message. It's the same message as always, with a few extra numbers attached, and it can be shown both ways from the same data.
Try this
Write a message, add a pause before the punchline, and play it back.