Measure the minimum amount of salt your are able to detect in water.
If you do this experiment with others, you can do a "blind tasting" and measure the detection threshold of each one of you as if you were laboratory instruments.
The human body is extremely sensitive to certain environmental variables. We can detect some odours and flavours in very low concentrations. You can start pouring 0.1 g of salt in 10 litres of water. Can you detect the salt? Test now 0.1 g in 1 litter. Not yet?