Penrose triangle
Three convincing corners. One impossible connection.

Arrows become contradictory solid forms.
View larger, then trace one connected edge all the way through the object. Compare the local joins with the whole shape.
Mabit1
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Download imageArrows become contradictory solid forms.
View larger, then trace one connected edge all the way through the object. Compare the local joins with the whole shape.
Follow the faces through each arrowhead and shaft. The solid interpretation of the connected parts is less consistent than the immediately recognizable symbol.