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: threatening behavior by predators causes a porcupine to extend its quills. 
Sentence2: Fishers are one of the few specialized predators on porcupines.
[A]: predators


[Q]: Sentence1: Insects have 2 antennae. 
Sentence2: Insects have 2 appendages to detect sound.
[A]: 2


[Q]: Sentence1: Echinoderms lack respiratory and excretory systems. 
Sentence2: Echinoderms in the diorama include the crinoids and blastoids.
[A]:
Echinoderms