Events, Triggers, and Explosions - Learning Game Physics with Bullet Physics and OpenGL - page 103

special case in order to generate an explosion somewhere on the ground plane's
edge; otherwise it would simply ignore them and we could only generate explosions
on the edges of the boxes. It's set to false by default, to spare us from having to
edit our existing calls to Raycast() .
bool Raycast(const btVector3 &startPosition,
const btVector3 &direction, RayResult &output,
bool includeStatic = false );