Reverse speech is a common occurence in everyday life. In fact, many scientists believe that babies first learn to speak backwards (goo goo ga ga? anyone?).
It can be done as a way of reaching the mind subliminally, or it can come out of you without you noticing it.
People form interesting habits in speech, I for instance speak in Iambic Pentameter like 60% of the time. I had no idea till someone pointed it out to me and I freaked out.