To avoid having any one element of foreshadowing be too obvious, often the writer will throw in some red herrings–some things that could be foreshadowing but in fact don’t pay off or pay off in a different way than we expect. The person who has the gun in the drawer may become an immediate suspect in our minds, but later maybe we see him use it to light his cigarette and we realize it’s not a real gun (of course he may have a real one somewhere else….). That kind of misdirection keeps the audience guessing.