Answer:
Increase; supply
Step-by-step explanation:
When the supply of the milkshakes increases then as a result there is an increase in the consumers surplus. This is due to the lower price level in the market of milkshakes. If there is an increase in the supply of a product then as a result this will reduce the equilibrium price level, therefore, the difference between the consumer's willingness to pay and actual amount paid for the product is greater.
When there is more supply than the demand for the product, the price of the product falls.