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.

[Q]: Sentence1: boiling means change from a liquid into a gas by adding heat energy. 
Sentence2: boiling changes a liquid into steam.
[A]: liquid


[Q]: Sentence1: hunting requires seeing prey. 
Sentence2: hunting requires seeing an animal.
[A]: hunting


[Q]: Sentence1: Reproduction is the process by which organisms give rise to offspring. 
Sentence2: reproduction is the process by which humans give rise to offspring.
[A]:
Reproduction