As one changes, the other should change, too. The implication is that eating while standing in front of the fridge causes you to gain weight. But in reality, people who eat in front of the fridge tend to grab more food and select food with less discrimination than people who select a meal and sit down to eat it. It could also be that those who eat in front of the fridge eat more often than those who sit down to eat. College graduates make more money than people without a college education.
Healthy cattle have more lice than cows that are sick.
You should be able to come up with several ways you can question these statements. These questions should point out that one does not cause the other. Graphs don't always tell the whole story. Sometimes graphs are constructed with a deliberate attempt to deceive. Always ask yourself what the graph isn't showing.