Coke: The Pause That Refreshes

The Los Angeles Times reports on a study of addictions in rats (probably the next focus in our War On Drugs):
In the experiment, 43 rats were placed in cages with two levers, one of which delivered an intravenous dose of cocaine and the other a sip of highly sweetened water. At the end of the 15-day trial, 40 of the rats consistently chose saccharin instead of cocaine.When sugar water was substituted for the saccharin solution, the results were the same, researchers said.

Did it ever occur to them that maybe the rats were just thirsty?