Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Sentence1: a sifter is used for separating mixtures. 
Sentence2: a sifter is used for some recipes.
sifter

Sentence1: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.
cold

Sentence1: Yeast reproduce asexually by budding. 
Sentence2: Yeast reproduces asexually by forming spores.

Yeast