Although my Mercury is in Taurus and retrograde, I find that I have always been able to quickly come up with elaborate lies on-the-spot when speaking to someone. I can also continue the lies throughout several encounters (as long as it's not been too long) and I am able to use different variations on the same lie for different people while keeping track of the degree of deception I have done to each person.
An example of a situation in which I would lie, would be if someone asked me where I grew up or how many children I have. I don't even want to divulge this basic information; I am very secretive. I don't like people prying into my business or being nosy (usually they want it as ammunition against me). Even worse is if people ask me about my political or religious views, or try to judge me (why I don't eat at restaurants, why I wear dresses, why I am so thin).
I have no Gemini in my chart and my mental speed is really quite slow. I can never come up with biting comebacks or stinging insults until days after an encounter. I am distractable with a terrible short-term memory. I have no Libra in my chart and do not seek ways to manipulate or mentally "play with" people. I just want to be left alone.
I wasn't able to understand this discrepancy until I read this interpretation from astrolibrary.org for Mercury SesquiSquare Pluto: "Mental intensity. Troubled mind. Passive-aggressive argument. Persuasive speech. Craftiness. Strategy. Paranoia." And there it is--I have Mercury opposite Pluto (0°07' orb) natally! I never would've guessed Pluto would produce this, as I thought only Gemini placements cause "trickster" traits or quick thinking.
How an aspect between two retrograde planets in Fixed signs allows me to figuratively do an octopus ink-spray to people, is still a mystery to me.