SEE would XOR the next word of data from an input stream into the given register. Running SEE in reverse does the same thing; the direction of flow of the input stream is not necessarily dependent to the direction of PC incrementing. Thus a subroutine that does SEE cannot generally be expected to clean up after itself properly by running it backwards.
SHOW would echo a copy of the given register to an output stream. (Ditto in reverse mode.) We don't want to erase the register, because the point of SHOW is to provide a way to view useful pieces of the state of the machine, not to provide a way to get rid of garbage data and its excess entropy. (Wait till the next section.)
Whether SEE and SHOW are reversible with respect to their effect on the outside world depends on the implementation. Neither need cause internal dissipation in the CPU.
SEE and SHOW will be useful for debugging Pendulum programs under a simulator.
Although the direction of the streams is not necessarily tied to the CPU direction, we may want to be able to reverse both at once in the overall debugging system.