Basic Recursion Problem I was doing some recursion review on CodeBat and this question's solution has been really confusing me.

The question was to write a recursion method that finds the number of bunny ears (double the number of bunnies entered).

The base case is 

if(b == 0){

	return 0;

}

the whole solution is 



}
	
	public static int bunnyEars(int b){
		
		if(b == 0){
			return 0;
		}
		
		return 2 + bunnyEars(b - 1);
		
	}

Why does the program know to stop if b goes under 0? Why do I not need an error check? Or am I just misunderstanding some part of recursion?