According to the Japanese psychiatrist Akioshi Kitaoka, this illusion must be fixed or move a bit for a calm, balanced, well rested man. If the picture is actively moving - you need a rest!
He'll receive a letter like this:
Subject: (Your friend's name), (Your name) here. Thought you'd like to see this website. Content: (Your Friend's name),I found this site I thought you'd like to see:
http://www.this page URL.ru Your friend, (Your name)