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: Insects have 2 antennae. 
Sentence2: Insects have 2 appendages to detect sound.

A: 2
****
Q: Sentence1: measuring the hardness of minerals requires scratching those materials. 
Sentence2: To figure out the hardness of a mineral, the Moh's scale of hardness is used.

A: minerals
****
Q: Sentence1: Bioterrorism is another potential threat in the environment. 
Sentence2: bioterrorism is silent.

A:
Bioterrorism
****