How to fix UnboundLocalError

[Tawnwen]

The code below models a simple game that tests if an input occurs in the list. The function is called twice, then the total # of correct answers is printed.

foot_bones = ["calcaneus", "talus", "cuboid", "navicular", "lateral cuneiform", "intermediate cuneiform", "medial cuneiform"]
answers_right = 0

def finder(bone_name):
    if bone_name.lower() in foot_bones:
        print("correct!")
        answers_right += + 1
    else:
        print("incorrect")
        
finder(input("enter name of a bone: "))
finder(input("enter name of another bone: "))

print("number of foot bones correctly identified: ", answers_right)

Code returns no error when the input is "incorrect", but gives an UnboundLocalError when a correct one is passed. How do I fix it? Simple issue.

Thanks!