Let's look at the picture below.

The wave in the sea has made Allen and Michael to feel nauseous.

 Things I need to check before making a causal claim

Causal claim (unstated) : The wave in the sea caused Allen and Michael to feel nauseous.
Cause : The wave in the sea.
Effect : Allen and Michael felt nauseous.

Cause and effect each happened? Yes

Cause precede effect? Yes
However, we need to find out whether Allen and Michael always feel nauseous every time when they are in the sea.

Cause makes a difference? It could be.  However, perhaps Allen and Michael were already feeling sick before encountering the wave?

Common cause? No. There may be other factors that could make them feel that way. 

Common cause? Need to investigate more before we can conclude on anything.