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) is clicked.
Blocks that look like this can be used to detect an event such as clicking on the sprite, pressing a key, or clicking the green flag button. They tell the script to start when that event occurs. Because these blocks can sit only on top of a script (as a way to start the script), Snap! programmers call them "hat blocks."
Clicking the green flag (
) starts all scripts that begin with the when green flag is clicked hat block. You can stop all running scripts by clicking the red stop sign (
) at the top right of the Snap! window.

say a welcome message whenever the green flag is clicked. (Alonzo might say, "Welcome to 'Click On Alonzo!' Keep clicking me if you can!") .
block with an empty input will make the sprite say nothing.