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: the uterus is used in reproduction.
Sentence2: Reproduction uses the same organ as menstruation.

Ex Output:
reproduction

Ex Input:
Sentence1: harming an animal species causes that animal 's population to decrease.
Sentence2: Wild animal populations have decreased drastically, due to both hunting and loss of habitat.

Ex Output:
animal

Ex Input:
Sentence1: Chromosomes are the form of the genetic material of a cell during cell division.
Sentence2: Microtubules move the genetic material of a cell during cell division.

Ex Output:
cell