Behold, a truly fantastic gift for the cat in your life — catnip-filled soft toys shaped like amoebas, cyanobacteria, and (pictured above) giardia.
Giardia are microscopic parasites that can invade the guts of vertebrate animals, including cats and humans. Generally, you get it by ingesting giardia-infested feces. For humans, this mostly means contaminated drinking water, because giardia are harder to kill than you might think. They can survive quite happily outside of a host and are resistant to chlorine.
Read more on giardia (and see pictures) at the CDC website