Puff up
Definition 1 of 2
Pro Tip 1/3Physical Change
Used when something physiologically expands due to air or gas. 
When startled, the pufferfish puffs up to appear larger.
Pro Tip 2/3Emotional Display
Can describe someone showing emotions like pride or anger. 
She puffed up with pride after receiving the compliment.
Pro Tip 3/3Visual Illusion
Used to mean making something look bigger than it really is. 
He puffed up the pillow to make the couch look cozier.