Yes, I know you might think that Taylor Swift is already very slim and she is but she is certainly using a trick that is good to highlight graphically.
The American singer is wearing this dress that makes her look much more slimmer.
The reasons are:
1. the dress is black and black is a slimming colour
2. the dress emphasizes her waist
look how those triangles bring your eyes towards her tiny waist and it even look smaller because those shapes reduce the size of her waist width.
This is another outfit that shows how you can emphasize your waist to look slimmer.