Be sure to save before trying these "interactive cut-scenes."
A few buttons will pop up on the screen, and you have to hit the correct button within a few seconds.
>>spoiler below<<<
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*Tomb of Tihocan*
Once you enter the tomb, save, then walk through a gap in the stone murals to the left, towards the next Scion piece. The cutscene will then begin.
Lara vs. Pierre: B, Y