What would happen if he said. "My nose will be growing now." ? His nose would either... A. Explode B. Cause a major rift in time and space C. Implode or D. Create a black hole.
E. Shrink, because he could have very well been telling lies beforehand and he didn't tell a li- WAIT WHA- *A B C D all at once*
The spell acts as a lie detector, not as a truth detector. If Pinochio was convinced, say, that 2+2=5 (false statement), or that there' s absolutely no task that an omnipotent God could not achieve (paradoxical statement), he could make those claims all day long, it wouldn' t make his nose grow. You can either believe a claim to be true or not believe it. These are the two only options, there' s no middle ground. In other words there is absolutely no situation that would require Pinochio' s nose to both grow and not grow at the same time.