Fact 1: Thirst is used to make an animal realize that it needs to replenish its bodily water by the body.

Fact 2: Water Water in the area's natural water bodies is drinkable as such.

Given the two facts above, answer the question "what is used to make an animal realize that it needs to replenish from a natural drinkable source" with the following options: 
- spring
 - excretion
 - blood
 - pain
 - thirst
 - tiredness
 - hunger
 - rain


 

     thirst    