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: Lymph is a fluid that leaks out of capillaries into spaces between cells. 
Sentence2: Humans are made up of trillions of cells.

A: cells
****
Q: Sentence1: Male dogs use pheromones in urine to mark their territory. 
Sentence2: Pheromones are hormones that are thought to stimulate, through smell, sexual reactions in animals.

A: pheromones
****
Q: Sentence1: a warm front causes cloudy and rainy weather. 
Sentence2: Behind the warm front are thick, low stratus clouds and possibly more rain.

A:
front
****