Last time when I saw her in a bikini I was wondering where Hilary Swank’s boobs
vanished, and to prove me wrong she came back with a fuller bra and showing a
little boob.

Well,
usually when a woman works out a lot, besides the fat from her body that it gets
burned, the fat from their breast gets burned too, loosing most of their breast
tissue, which is being replaced with muscle, but not in the same quantity. So
this can be a good reason why Hilary Swank has smaller boobs than she use to
have.