While creeping through the Training Facility, Rebecca is attacked by the Eliminators released by the mysterious young man. Just as she is about to recompose herself, the floor collapses and Rebecca is swallowed by the resulting void.
The player is given control of Billy, who has to make it to the basement where Rebecca is hanging on for dear life. This part of the game is on a timer however, and the wick is pretty short.
The first time I played I wasn't able to save her, even though I was quite fast; it certainly stands out as one of the game's tougher challenges, I wonder how many people made it down there the first time they played?
Still Rebecca's definitely got some muscle on those arms seeing how long she can hold out, she isn't in S.T.A.R.S. for nothing.