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: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Water freezes into ice when cooled.
freezes

Sentence1: Antigens are proteins foreign to the body. 
Sentence2: antigens are proteins.
proteins

Sentence1: Protists are single celled organisms containing organelles. 
Sentence2: slime molds are fungus-like single celled organisms.

celled