Stage 5: refactoring. When I run app on emulator I get first fact then when I keep clicking button nothing comes up.

import java.util.Random;

/**
 * Created by Hamish on 2/09/2014.
 */
public class FactBook {

    // Member variable (properties about the object)
   public String[] mFacts = {
            "Ants stretch when they wake up in the morning.",
            "Ostriches can run faster than horses.",
            "Olympic gold medals are actually made mostly of silver.",
            "You are born with 300 bones; by the time you are an adult you will have 206.",
            "It takes about 8 minutes for light from the Sun to reach Earth.",
            "Some bamboo plants can grow almost a meter in just one day.",
            "The state of Florida is bigger than England.",
            "Some penguins can leap 2-3 meters out of the water.",
            "On average, it takes 66 days to form a new habit.",
            "Mammoths still walked the earth when the Great Pyramid was being built."};

    // Method (abilities: things the object can do)
    public String getFact() {

        String fact = "";

        // Randomly select a fact
        Random randomGenerator = new Random(); // Construct a new Random number generator
        int randomNumber = randomGenerator.nextInt(mFacts.length);

        fact = mFacts[randomNumber];

        return fact;
    }
}

package com.example.hamish.funfacts;

import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.Random;


public class FunFactsActivity extends Activity {

    private FactBook mFactBook = new FactBook();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fun_facts);

        // Declare our View variables and assign them the Views from the layout file
        final TextView factLabel = (TextView) findViewById(R.id.factTextView);
        Button showFactButton = (Button) findViewById(R.id.showFactButton);
        View.OnClickListener listener = new View.OnClickListener() {
            @Override
            public void onClick(View view){
                String fact = mFactBook.getFact();
                // Update the label with our dynamic fact
                factLabel.setText(fact);
            }
        };
        showFactButton.setOnClickListener(listener);
    }
}