Reminds me of that Colorado Uni study...
Flushing the toilet lidless could make you sick, researchers find
In a new experiment using bright green lasers and camera equipment, scientists from Colorado Boulder University were able to visualize airborne particles, invisible to the naked eye, that are shot into the air when a lidless toilet is flushed.www.ctvnews.ca
If you close the lid you just pressurize the contents and add extra force to it.