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: Combustion-related, motor vehicles, wood burning, open burning, industrial processes. 
Sentence2: Combustion is used to produce heat.

Ex Output:
Combustion-related


Ex Input:
Sentence1: Sperm pass out of the body through the urethra. 
Sentence2: Sperm travel from the testicles through the vas deferens to the seminal vesicles and the prostate.

Ex Output:
Sperm


Ex Input:
Sentence1: a firecracker converts chemical energy into sound. 
Sentence2: a firework converts chemical energy into sound.

Ex Output:

chemical