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: Bees feed on nectar and pollen. 
Sentence2: Plant reproduction often requires bees and nectar.

Ex Output:
Bees


Ex Input:
Sentence1: a mutation in the sex cells of a parent can cause a new trait to appear in the parent 's offspring. 
Sentence2: Traits are initiated by mutation and recombination.

Ex Output:
mutation


Ex Input:
Sentence1: Since heat moves from where it's warmer to where it's colder, the thermal energy in the air transfers into the cooler liquid. 
Sentence2: heat moves from a warmer object to a cooler object when the two objects touch.

Ex Output:

heat