Now that you've learned how to use Sprite Lab,
you're going to want to make your program react
when someone plays with it.
To do that, you're going to use events.
Blocks like `when clicked` and `while touches` are called event blocks.
The code connected to an event block
runs when the approprite input,
like a click or a tap, is detected.
For example, if you attach this `change size by` block
to the `when Alien 1 clicked` event the sprite will change size when it's clicked.
Notice that event blocks don't snap into your main program.
Instead, they create little programs of their own.
Remember that even if the event only happens one time,
behaviors will go until you stop.
You can use a `stops` block
if you don't want multiple events to combine behaviors.
Using events, you can create imaginative programs
and interactive worlds.
Give it a try!