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This is a prime example of what I call the Japanese cleavage enhancing pose (I swear this image is somewhere on my blog, but I can't find it).
The 2 parts of this tactic:
1) Bend forward (and down), so gravity gives you a boost
2) Subtly use your upper arms to squeeze inwards so your mass is consolidated
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Notice how here one's arm can serve as a subtle pushup bra