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: Examples of gametes are ova and spermatozoa. 
Sentence2: fertilization of ova and spermatozoa produces a diploid zygote.

Ex Output:
ova


Ex Input:
Sentence1: Hair helps to insulate and protect the body. 
Sentence2: most mammals have insulation that also protects the body.

Ex Output:
body


Ex Input:
Sentence1: Sound Sound waves are mechanical waves. 
Sentence2: the type of material through which mechanical waves pass change the speed at which they travel.

Ex Output:

mechanical