The Boulder was always a famous trap in the Tomb Raider Games. The boulder on the right is actually a Rolling Ball, there are also other boulders that are not spherical.
Prior to Last Revelation, the balls are not physics based, and will only roll in one direction at a constant speed, until they hit a ledge, wall, or a slope that faces the other way. However in the fourth game it is physics based and it bounces and rolls according to the terrain.
Boulders always kill Lara instantly unless she is in a vehicle. She only bleeds extensively in the first three games when flattened by a boulder.
- Tomb Raider