If [one, for some reason], needs to talk with [the aforementioned antagonistic individual] concerning a matter of necessity, he should shorten the amount of time that he stands with him [involved] in this [conversation]. For, [if he would not shorten the discussion as much as possible], he will thereby definitely, come [to be involved in] Lashon HaRa. [This situation resembles] the gunpowder which gives off the scent of fire [when ignited], it being impossible that this [igniting of the gunpowder] will not result in a flare [of fire].
 The passage from the gemara in maseches Arachin, states as follows:
“Rav Dimi, the brother of Rav Safra, taught, “A person should never speak about the good of his friend, for due to speaking about the good [aspects] of his friend, he will come [to speak of] the negative [of his friend].” There are those who say [the incident occurred as follows]: Rav Dimi the brother of Rav Safra was sick. Rav Safra came to visit him. [Rav Dimi] said to him, ‘Come down to me, for I fulfilled all of the Rabbinic laws. [Rav Safra] said to him, “Did you ever follow [the teaching] that a person shouldn’t speak of the good [aspects] of his fellow, for as a result of speaking about that which is good about him, [people] come to speak shamefully against him.” [Rav Dimi] said [to Rav Safra], “I didn’t hear of this, but if I would have heard of it, I would have fulfilled it.””
RaSh”I comments on this gemara that, due to praising the individual, either the person who is praising the individual will say, “This person has only good qualities, with the exception of this bad quality”, or other people will point out something negative about the person being praised – “Doesn’t he have such-and-such negative qualities?”
Thus, a person should be careful to avoid praising someone in a way that may lead to others disparaging him.
 The analogy of igniting gunpowder teaches of the caution one must take when speaking with someone who bears a grudge against his fellow. The person should not prolong the conversation with this individual who bears hatred against his fellow, and should limit the conversation to only that which is essential. Otherwise, he may arrive at a situation where the other person begins speaking Lashon HaRa against his fellow. Once gunpowder is lit, it will flare up, so too, once the other person has an opportunity to turn the conversation against the one whom he hates, Lashon HaRa will inevitably follow, chas v’shalom.