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: hurricanes convert heat energy into mechanical energy. 
Sentence2: Hurricanes use heat to move objects.
hurricanes

Sentence1: Coral reefs are made up of the accumulated exoskeletons of the coral polyp. 
Sentence2: coral polyps form reefs.
polyp

Sentence1: Muscles can only contract. 
Sentence2: Smooth muscles are involuntary muscles.

Muscles