I used a quill-esque pen which I've had for years; it was a part of an art set I got when I was a kid where you scratch out a black board and draw pictures (does anybody know what I'm talking about?) but you could easily substitute with a toothpick or a fine nail art brush if you have one.
I did this freehand and it does take a bit of practice but you could stencil it out by using tape and outlining the shape.
- Apply base coat and dry
- Using a white nail polish, follow the above diagram and dry
- If necessary, repeat step 2 to get an opaque layer
- Draw 2 black dots for eyes using a dotting pen (or toothpick)
- Put a blob of pink nail polish onto a piece of paper
- Dip the quill (or toothpick) into the white nail polish and draw 3 triangles onto the cat for ears and a nose
- Draw 2 black lines horizontally from the nose outwards on each side of the nail for whiskers using the dotting pen (or toothpick)
- Let everything dry
- Seal it all with a top coat