false
叚 centers on falseness or pretense: something that is not genuine, counterfeit, or deceptive.
The historical development of 叚 is uncertain. It appears as a component in other characters, but its independent origin is not clearly established.
The shape suggests a hand (又) over a mouth (口) with a cover (一), like someone hiding the truth behind a false front.
For カ, imagine a false car salesman selling a fake vehicle: car -> カ, and the deal is false.