Kind of a dumb question, but I can't see it covered in the WCA regs anywhere... During feet solving, is there a rule that says what the competitor may have in their hands? Specifically, is the competitor allowed to have another cube in their hands, and if so, are they allowed to carry out moves on it?
D1) Standard speed solving procedures are followed, as described in Article A (Speed Solving)
A5b) While inspecting or solving the puzzle, the competitor must not receive assistance from anyone or any object other than the surface (also see Regulation 2i). Penalty: disqualification of the attempt (DNF).
I don't know if holding a cube is assistance, but I think doing turns on it is