"Frames" move in one directon and squares in another.
<p>NOTE: You'll need a second image to activate this illusion:
</p>
<a href="//commons.wikimedia.org/wiki/File:Moving_illusion_catalyst.png" title="File:Moving illusion catalyst.png">File:Moving_illusion_catalyst.png</a>
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<span class="int-own-work" lang="en">Own work</span>