How is collision calculated?

[ole92]

Hello there,

I'm really impressed with the collision detection and general physics in penumbra.
Could someone tell me how it's done, especially the part where I'm holding something with the left mouse button, and try to collide it with a wall.

I'm making my own game, and having some difficulty, when objects that I'm holding, can go through other objects.
This only happens when I'm holding them...

Thanks