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: Leeches are external parasites. 
Sentence2: Leeches live on the surface of their hosts.
Leeches

Sentence1: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: Fossils of a water animal or plant are located in water-laid sediments.
animal

Sentence1: when sound reaches the ear , that sound can be heard. 
Sentence2: When vibrations reach the ear, music can be heard.

ear