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: a pulley is used for lifting objects. 
Sentence2: Resistance exercises are weight-lifting exercises.
lifting

Sentence1: hunting requires seeing prey. 
Sentence2: hunting requires seeing an animal.
hunting

Sentence1: After a six month gestation, a female gives birth to a single offspring, sometimes to twins. 
Sentence2: Reproduction is the process by which organisms gestate offspring.

gestation