I have developed this theory called 'The Thirst Theory'. It states that "If a person sees a bottle of water in the middle of a discourse, that person feels thirsty." The discourse here applies mainly to classroom lectures. It has been proved beyond doubt in the last 5 years.
A typical experimental proof goes something like this. A specimen will make it known to all other specimens that he/she is drinking water. Subsequently, thirst levels start going up in surrounding specimens. Somewhere far away, a particular specimen's thirst will cross the threshold level and he/she will solicit the container of water. But as the container of water begins its journey across the class, the threshold of specimens in its vicinity is immediately crossed (something like the 'Lord of the Rings'... the water bears its influence on those who carry it) and they drink of that precious little that remains. The value of water goes on increasing as it inches closer and closer to its real destination. As it reaches the intended specimen, there is little left, and the specimen relishes each drop.
Funny but true. Check it next time someone drinks water in class.