Most flies can only eat liquids. Then why do they land on the bread of your sandwich?
Answer:
When a fly lands, it regurgitates some of its last meal, along with digestive juices. That partially dissolves dry food, allowing the fly to then slurp up the liquid. That mix is what causes the "fly specks" that are sometimes left on windows. Just try not to think about what that fly's last meal might have been, especially on your sandwich.
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