[card_zero]

I think the way to construct these is: find (a) such that all kinds of things can cause it, choose (b) as one of the causes of (a), choose (c) as something else also caused by (b) but also having all kinds of other potential causes different from those of (a).

So this example isn't good, because when people are eating most ice cream, people are using most air con, both being mainly caused by hot weather. (Unless as you point out we're looking at one individual who wants a solution to feeling hot and doesn't need to do both things together.)