Thou shalt not reply if thou art replying to a post that is replying to one of thine own.
For example, if Fred, Daphne and Wilma are playing the Worde Association Game, then the following example wouldst be illegal;
Fred has violated the rule, and shall have to be flogged! Well, maybe not flogged, but thou gets the idea.
The following exchange, however, wouldst be acceptable;