def count_vowels(word):
    """
    This function takes a word and returns the number of vowels in that
    word.
    """
    count = 0
    for letter in word:
        if letter=="a" or letter=="e" or letter=="i" or letter=="o" or letter=="u":
            count = count + 1

    return count
        
### To test:
print "mouse has " + str(count_vowels("mouse")) + " vowels"
print "dog has " + str(count_vowels("dog")) + " vowels"