Quote Originally Posted by oldboy
Quote Originally Posted by Lynn
Does that help?
And how! Thank you, Lynn.

And is "in what" used only in passive constructions or it's possible to use it in active too?
For example, In letter I often use in what everybody calls 'smilies'.
Both passive and active are okay, but it's good that you asked. It made me realize that there's something I should have explained better. The construction is not "in what," it's just "what." The "in" was used because it is connected to the passive construction using "poisoning." ("in the poisoning")

So your active example should be:

In letters I often use what everybody calls 'smilies.'

So sometimes you don't need a preposition: She wrote what eventually became a famous novel. (She wrote a novel = no preposition.)

And sometimes you do need a preposition. I was bitten by what turned out to be a poisonous spider. (I was bitten by a spider = preposition.)

Again this reminds me of который. Sometimes you don't need a preposition and sometimes you do, depending on the sentence:
Мы говорили о студентах, которым мы помогали прошлым летом.
Мы говорили о его сестре, с которой мы познакомились в среду.