In 4-1, you'll encounter a gate that requires a key. The key is on a platform to the left, and the gate is to the right. To get the key, you must move left. However, moving left rewinds time. The solution is to first walk to the right, past the gate, then turn around and walk left to collect the key. As you walk left, time will rewind, but you will retain the key. Once you have the key, walk right again to the gate, and it will open. This puzzle teaches you that items collected while moving left are kept, even as the world rewinds around you, allowing for strategic item acquisition.
