Hey,

I found out the answer . For future readers, my mouth (the pacman's) is a triangle, so we need to know if a point is inside a triangle. To do this follow these steps:
Code:
1) Get the formula for the area of a triangle given the three vertices.
2) Calculate the area of the triangle.
3) Use the point as a new vertix and calculate the areas of the three
triangles formed by the point and the three sides of the original triangle.
4) If the sum of the areas of those three triangles is the same as the area
of the original triangle, then the point is within the triangle. If the sum
is greater, the point is outside the triangle.
bye