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.

Sentence1: a wildfire changes an ecosystem drastically. 
Sentence2: Forest fires change an ecosystem drastically.
changes

Sentence1: Aggression is behavior that is intended to cause harm or pain. 
Sentence2: Verbal violence is behavior that is intended to cause harm or pain.
behavior

Sentence1: Rainy clouds cause rain, and excess water vapor from clouds is the basis of rainbows. 
Sentence2: Condensation can lead to rain.

rain