The big problem with a sneeze is getting the angle lined up with your center of gravity. The regular way of sneezing would impart more angular than linear motion. You have to tilt your head way back, etc. And for an involuntary reflex like sneezing that’s not easy to do.
(Keep in mind that prior to the sneeze you need to inhale in the opposite direction.)
Note that it’s far harder to adjust the angle at the other end. OTOH, it’s sort of already lined up and the CoG can be adjusted by bending.
And the problem with farts is doing them while wearing pants, which contain the momentum within the astronaut/pants system. Accleration would have to happen with a pantless farting astronaut, though too little to notice.
And now I’m going to contemplate all my life choices that led to my writing the above paragraph.
Pretty clearly what is called for is some sort of tubular extension that can redirect the force of the nasal or anal blast without attenuating it too much.
Gives a whole new meaning to “set her down on her nose jets.” Or Tail Jets.
Have you never seen Thunderpants?
I have to imagine, pantless or no, the other ISS astronauts fought vigorously to prevent any in-depth testing of the hypothesis.
Well that just stinks.
Somebody had to say it…
Some knowledge comes at too high a cost.
If I may ask a follow up question. . . If you light farts in Zero-G, what shape does the flame take?
Ask Grissom, White, and Chaffee.
Still too soon, man. 
Not to mention the rocket was still on the ground.
Now, if the line had been, “Ask Christa McAuliffe…”
Okay, it’s time to go back to kunilou.
So would the fart be ejected in a teardrop shape? and then roll around as a sphere before it dispersed?
In my case I would need a seat belt on the commode.
The toilet on the space shuttle actually has a seat belt, but not because of flatulence-induced motion. Ordinary movements are enough to cause trouble:
There are 2 things wrong with the study that lead to the quoted conclusion:
- Wrong point of view
- Zero gravity is an unnecessary and complicating variable
I have taken part in many, many studies that have all come to the same, repeatable conclusion: propulsion by fart is not only possible, it is a fact.
Study set up: a semi-enclosed room
Participants: me plus N other living beings
Study execution: I fart
Study results: In every case, all N other living things move quickly toward the exit(s)
Study conclusion: farts do indeed propel living things
Anyone wishing to serve as a volunteer “N” subject for future experiments should contact me. Or your psychiatrist.
Darren Garrison, just so you know; I literally giggled aloud for about three minutes after reading this.
Couldn’t we just conduct all these experiments on the Vomit Comet? We don’t really need to stink up the ISS doe we?