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: Sperm had to swim from male to female reproductive organs for fertilization. 
Sentence2: If fertilized, the egg implants itself in the uterus.
fertilization

Sentence1: Dams are very damaging to rivers. 
Sentence2: Creating a lake can be very damaging to rivers.
damaging

Sentence1: Mynah birds are the main competing species for nest holes. 
Sentence2: Mynah birds undergo specialization to compete for nest holes.

Mynah