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.

Example Input: Sentence1: After about a week the larvae leave the nodules and continue to develop into adult worms. 
Sentence2: larvae leave the nodules and continue to transform until having reproductive organs.
Example Output: larvae

Example Input: Sentence1: Cell death occurs by activation of cell death genes. 
Sentence2: Aging is associated with the activation of certain genes.
Example Output: activation

Example Input: Sentence1: Hemoglobin transports oxygen in blood. 
Sentence2: breathing is when a gill converts from oxygen in water into Hemoglobin.
Example Output:
Hemoglobin