The thing about a shark is—teeth,
One row above, one row beneath.
 
Now take a close look. Do you find
It has another row behind?
 
“About the Teeth of Sharks”
John Ciardi

[This photograph shows inclusions in a round glass fishing float. These devices were once used by fishermen worldwide to keep their nets afloat in the ocean. Many fishing floats are still adrift. Some eventually wash ashore and become collectors’ items.]