There has been speculation that Hans Landa puts out the cigarette on the strudel to make a reference to the LaPedite cabin which had a chimney.
I had not seen compelling evidence to make a strong argument for it, but I was just remembering that as Tarantino developed the character with Christopher Waltz they were going over the initial interrogation scene when they decided that Landa doesn’t really smoke.
The big calabash pipe he takes out is a deliberate use of a prop as part of his theatrical interrogation tactics, everything he does and says has a purpose, to intimidate, coerce, manipulate, and so on.
He researches everything and knows LaPadite does smoke a pipe so he brings a bigger one both as a power move and as a Sherlockian symbol of his detective prowess.
So if he doesn’t smoke why did he bring out cigarettes?
I went back to the strudel scene and noticed that right after he lights one for Shosanna and then one for himself only a few seconds pass before he puts it out.
The ashes on his cigarette also show very little consumption (actually more than could be expected for the 3 seconds that elapse, but still 80% left of it, practically new.)
If he is someone who always operates meticulously under the capacity of a proud detective this seems to be strong evidence of utilizing cigarettes as a prop, and the fact that he is someone who finds humor in his work and delights himself by toying with his interrogation subjects makes me think the act could be indeed a playfully evil reference to the massacre for his personal amusement.