In this food themed riddle, when are you supposed to "stop at green and go at red" even though traffic lights usually mean the opposite?

Introduction / Context:
This riddle uses the familiar rule of traffic lights, where drivers are taught to stop at red and go at green, and then cleverly reverses that logic in a different everyday context. The wording asks: "When should you stop at green and go at red?" At first it seems impossible, because it contradicts our road safety rules. The trick is to recognise that the riddle is not about driving at all. Instead, it refers to colours found in food, specifically in a fruit where the outside and inside have opposite traffic light colours.

Given Data / Assumptions:

• The riddle explicitly mentions "green" and "red", which are traffic light colours but also common food colours.
• The phrase "stop at green and go at red" implies a situation where you interact with something green on the outside and red on the inside.
• The options include: When eating a watermelon, When driving at night, When playing a board game, and When planting a garden.
• We assume normal traffic rules: red means stop, green means go in driving.
• The puzzle is designed to lead you away from driving and toward another familiar context.

Concept / Approach:
The main idea is that certain fruits, especially watermelon, have a green outer rind and a red inner flesh. When you eat a watermelon correctly, you eat the red part and do not eat the green rind. So you "go" at the red part by eating it and "stop" at the green part by not eating beyond it. This reverses the traffic light rule in a playful way but fits perfectly in the context of food. None of the other options has a standard or widely known rule involving stopping at green and going at red that matches this level of wordplay.

Step-by-Step Solution:
Step 1: Notice that the riddle likely uses "green" and "red" symbolically, not literally as traffic signals. Step 2: Think of common objects that are green on the outside and red on the inside. Step 3: Recognise that watermelon has a green skin and a red juicy interior, making it an ideal candidate. Step 4: Apply "go at red": when you eat watermelon, you eat the red flesh enthusiastically. Step 5: Apply "stop at green": you stop when you reach the hard green rind, which is not generally eaten. Step 6: Check the other options. Driving at night still follows normal traffic light rules; board games and gardening do not have famous "green vs red" instructions that flip the usual rule in this way. Step 7: Conclude that the only situation where stopping at green and going at red is natural and logical is eating a watermelon.
Verification / Alternative check:
To verify, imagine physically eating a slice of watermelon. You start at the red portion and keep eating (go at red). As you get closer to the rind, you stop eating when you reach the green part (stop at green). This provides a simple and exact mapping from the riddle line to real world behaviour. No other listed context regularly involves people doing the opposite of the traffic light colours in such a clear and widely recognised way.

Why Other Options Are Wrong:
When driving at night, you still must obey traffic signals as usual, so you never intentionally go at red and stop at green. Board games might involve coloured pieces or squares, but there is no standard game where green always means stop and red always means go. Planting a garden might involve green plants and red fruits or flowers, but there is no simple, famous rule connecting those colours to stopping and going in the way the riddle describes. Therefore, those options do not satisfy the clever reversal built into the puzzle.

Common Pitfalls:
A common mistake is to remain stuck in traffic thinking, trying to interpret the riddle in terms of driving or road signs. Another pitfall is overlooking the connection between the colours and common foods. When solving riddles, it helps to zoom out and ask in what other contexts the same colour words could apply. Once you shift your focus from roads to food, watermelon quickly comes to mind and the answer becomes obvious.

Final Answer:
You should "stop at green and go at red" when you are eating a watermelon.