Why do we salivate during a nap of day time ?

Explanation

1) Nocturnal animals are during nights but we are active during daytime and take rest at night.
2) All the systems of our body are active in function during daytime of our activity. Hence ,man is a diurnal animal .
3) Our digestive system is also active and ready to receive the food for digestion .
4) If we sleep during daytime saliva oozes out of our mouth and wets the pillows .
5) This will not happen during night time.