Dissolve a quarter of a teaspoon of salt in 200 ml of room-temperature water.
Put 100 ml of the solution in one glass, and the other 100 ml in another.
Add a pinch of MSG to one of the glasses.
Taste the glass that doesn't have MSG in it, and note the level of saltiness you taste.
Rinse your mouth with fresh water.
Taste the water that has MSG in it, and compare the sensations.
The MSG water should taste saltier, and should also have an umami flavour to it.
This experiment was originally proposed by Anna and David Kasabian in The Fifth Taste: Cooking with Umami.
Verdict: The presence of MSG makes salty flavours more prominent.