diff --git a/demo/src/main.c b/demo/src/main.c
index 7b363ff..e22c2bd 100644
--- a/demo/src/main.c
+++ b/demo/src/main.c
@@ -52,8 +52,11 @@ void draw() {
 
 	if (mouseWentDown("left")) soundPlay(beep, FALSE);
 
-	groupCollideBetween(movement, 1);
-	groupPushGroup(edges, movement, 0.9);
+	int collision = FALSE;
+	if (groupCollideBetween(movement, 1)) collision = TRUE;
+	if (groupPushGroup(edges, movement, 0.9)) collision = TRUE;
+	
+	if (collision) soundPlay(beep, FALSE);
 
 	drawSprites();
 
diff --git a/src/collider.c b/src/collider.c
index 4113881..142639b 100644
--- a/src/collider.c
+++ b/src/collider.c
@@ -205,8 +205,8 @@ int heliCheckCollision(
 	
 	double kn = *vx*nx + *vy*ny;
 	if (kn < 0) {
-		*vx -= 2*kn*fabs(bounciness)*nx;
-		*vy -= 2*kn*fabs(bounciness)*ny;
+		*vx -= kn*nx*(1 + fabs(bounciness));
+		*vy -= kn*ny*(1 + fabs(bounciness));
 	}
 	
 	return TRUE;