This rat is being deprived of restful REM sleep by a researcher using the flowerpot technique. The water is within 1 cm of the small flowerpot bottom platform where the rat is standing. At the onset of REM sleep, the rat would either fall into the water only to clamber back to its pot to avoid drowning, or its nose would become submerged into the water shocking it back to an awakened state.
The Flowerpot technique is used in sleepdeprivation studies. It is designed to allow NREM sleep but prevent REM sleep. A laboratory rat is placed on top of an upside down flowerpot which is placed in a bucket of water. While in NREM sleep the rat retains muscle tone so it can sleep on top of the flowerpot. When the rat enters REM sleep it will lose muscle tone and fall off the flowerpot into the water, then climb back up and re-enter NREM sleep.