TASK DEFINITION: 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.
PROBLEM: Sentence1: Heterotrophs are living things that cannot make their own food. 
Sentence2: food contains organic molecules.

SOLUTION: food

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

SOLUTION: sifter

PROBLEM: Sentence1: competition may cause animals to fight towards members of their own species. 
Sentence2: Humans are animals too.

SOLUTION:
animals