Which psychological innovation was intentionally incorporated into shopping cart design to increase consumer purchases?

Consumer psychology plays a crucial role in retail design and product placement. One of the most studied elements in retail environments is the humble shopping cart, which has undergone significant psychological engineering to maximize purchases. Test your knowledge about how retailers use psychology to influence consumer behavior through cart design and implementation.

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Expanding capacity during shopping (carts designed to be easily expandable as customers shop)
Transparent baskets (to create social proof by showing other shoppers what you're buying)
Sound-dampening wheels (to reduce awareness of time spent shopping)
Temperature-controlled handles (warm handles to create comfort and extend shopping time)