TASK DEFINITION: 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.
PROBLEM: Sentence1: Sponges are filter feeders. 
Sentence2: Hawksbills feed primarily on filter feeders.

SOLUTION: feeders

PROBLEM: Sentence1: Nonmetal elements are far fewer in number. 
Sentence2: There are 17 nonmetals on the periodic table.

SOLUTION: Nonmetal

PROBLEM: Sentence1: Caecilians can be found in moist soil near rivers and streams in tropical regions. 
Sentence2: Caecilians are primitive amphibians that resemble earthworms.

SOLUTION:
Caecilians