Step 1: Open the original image, select the ellipse tool in the toolbar and frame the mouth.

Step 2: Right-click the picture and select Feather.

Step 3: Set the feathering radius to 30 pixels (it can be adjusted according to your own needs).

Step 4: Open the filter/twist/squeeze.

Step 5: Squeeze out the value inside, which can be changed according to your own needs. You can change it again and again here until you are satisfied.

Step 6: Open the selection. Click to deselect.