Related Clues:

• Go slow, entering sunbeam -- this doesn't happen often
• Fish circling river -- it's not a common thing
• Tub removed from tributary - it's a collector's item
• Once-in-a-blue-moon occurrence
• A slowing down in network is no common occurrence?
• Scarce item
• Track going round a river -- it's something unusual
• Curiosity of artist right before thing with unknown
• Wonder when 2, all but its first and second failing