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 Input:
Sentence1: freezing means changing from a liquid into a solid by reducing heat energy. 
Sentence2: Water freezes into ice when cooled.

Ex Output:
freezing


Ex Input:
Sentence1: Thrinaxodon, a small Lystrosaurus Zone cynodont, shows many of the characters of the group. 
Sentence2: Thrinaxodon is from the animal family that eventually evolved into mammals.

Ex Output:
Thrinaxodon


Ex Input:
Sentence1: a plant requires food for survival. 
Sentence2: Plants require photosynthesis for survival.

Ex Output:

plant