2 employees were working on an attachment to a skid steer. The attachment was removed from the bucket and set on 4X4's. A 3rd employee came to help and after one end of the attachment slipped off of the 4X4 the 3rd employee tried to reposition the 4X4 as the 1st employee slid the attachment back on the boards and this smashed the employee's fingers between the 4X4 and attachment.