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: heating an egg causes a chemical reaction in the egg. 
Sentence2: Insects hatch from eggs.
egg

Sentence1: Tree-ring dating the 1700 Cascadia earthquake. 
Sentence2: estimating the age of trees can be used in reviewing earthquake history.
earthquake

Sentence1: Birds move their wings using muscles in the chest. 
Sentence2: Birds also steer by changing their wing configuration.

Birds