Spoiler spoiler alert: you can however lock two carts to each other, though it is a bit of work! I never tested more than two, but the geometry of the situation would make it moderately difficult.
Not with the ones I've seen in NL, unless you put one cart on top of the other and turn it upside down. Indeed, that's a bit of work, lifting one cart (or pushing both carts flat on their side).
