Bottom 廾 depicts two hands held up together - the indexing radical. In full 開 these hands lift the bar away from the gate. Stripped of the gate by the 1956 reform, 开 now shows just hands lifting a bar. Same component in 弄, 弊, 异.
Top horizontal stands for the door-bolt being lifted off - in the traditional 開, the inside was 門 (gate) plus 幵 (parallel hands removing the bar). Simplified 开 kept just the bolt-bar plus the two hands beneath, so this stroke is the lid coming off.
