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: plant requires seed dispersal for reproduction. 
Sentence2: plants are pollinated by birds.
plant

Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: Allergens can trigger asthma attacks.
allergen

Sentence1: Animals can communicate with sounds, chemicals, or visual cues. 
Sentence2: cats can communicate with sounds, chemicals or visual cues.

chemicals