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: if a habitat can no longer support animals then those animals will move to another area. 
Sentence2: Each species of animal is unique.

Ex Output:
animals


Ex Input:
Sentence1: the mass of a planet causes the pull of gravity on that planet. 
Sentence2: the mass of a planet is what causes things to have weight.

Ex Output:
mass


Ex Input:
Sentence1: Insects have 2 antennae. 
Sentence2: Insects have 2 appendages to detect sound.

Ex Output:

2