You need to make sure to click on the input and select the sound you want to be played.
Off topic
You can actually use scratchblocks in the forum without using images. Just do this
[scratchblocks]
when flag clicked
forever
play sound [test v] until done
end
[/scratchblocks]
when flag clicked forever play sound [test v] until done end
More info here Snap [scratchblocks] Tutorial (Part 1)