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: Light source is an ultra-bright, unbreakable LED Bulb. 
Sentence2: LEDs convert electricity into light and heat energy.

A: LED
****
Q: Sentence1: the digestive system breaks food into nutrients for the body. 
Sentence2: Meat is a nutrient-dense food.

A: food
****
Q: Sentence1: ice wedging is when ice causes rocks to crack by expanding in openings. 
Sentence2: Water expands as it freezes into ice.

A:
expanding
****