[jwsea55]

The red dot on the moving chart is supposed to represent where the center of mass is moving. The blue on the spring represents the compressed part.

[KittenClaws]

The red dot on the moving chart is supposed to represent where the center of mass is moving. The blue on the spring represents the compressed part.
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I watched it again and you're right. But, the blue and the red dot meet the end at (seemingly) the same moment.