People do experiments on rats, you know, but not all of them are horrible, and some are very interesting. (Don't ask me about Learned Helplessness, though.) Apparently they once decided to see what sort of light levels rats preferred by putting them in cages with dimmer switches. Rats being rats they learnt how to use the switches and if put in a dark cage would turn the light up, or down if in a bright one. The experimenters took note of the light level which the rats chose. When they put the rats in a cage already lit at that level they found that the rats nonetheless altered the light level, randomly up or down. Essentially rats don't want any specific measurable light level, what they want is a level which they themselves have chosen.
I think this is great; it's like the Wife of Bath's tale but with rodents. Still it does make it harder to give them antibiotics. If you start a fight with a rat you've already lost. But don't assume that the rat or other pet doesn't know this -- our dog Peggy used to pretend she loved being wormed but secretly dribble the pills out of the corner of her mouth about ten minutes later so eventually you found them stuck to the side of the sofa or on your sock and had to go through the whole thing again. If they even realise there's the slight possibility of a fight you may already have lost. I'm doing OK getting antibiotics into Lilian at the moment because we have come to an agreement concerning antibiotic-soaked jaffa cakes, and because I am nonchalantly pretending I don't really care either way.