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: Mollusks are invertebrates such as the common snail.
Sentence2: Another common snail is the decollate snail.

Ex Output:
snail

Ex Input:
Sentence1: friction causes the temperature of an object to increase.
Sentence2: When we increase the temperature of objects, they always expand.

Ex Output:
increase

Ex Input:
Sentence1: erosion causes a river to become deeper and wider.
Sentence2: Fertile topsoil is then lost in erosion.

Ex Output:
erosion