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.

[EX Q]: Sentence1: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Water freezes into ice when cooled.
[EX A]: freezes

[EX Q]: Sentence1: a mutation in the sex cells of a parent can cause a new trait to appear in the parent 's offspring. 
Sentence2: cancer of a parent's cells can cause a new trait to appear in their offspring.
[EX A]: appear

[EX Q]: Sentence1: Eggs are usually laid in a nest. 
Sentence2: birds usually have nests.
[EX A]:
nest