Teacher: 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.
Teacher: Now, understand the problem? If you are still confused, see the following example:
Sentence1: pesticides cause pollution. 
Sentence2: pollution can harm animals.
Solution: pollution.
Reason: The word "pollution" is common to Sentence1 and Sentence2. So, it's a good answer.

Now, solve this instance: Sentence1: Light rays are focussed on the retina. 
Sentence2: When rays are shined at the eyes, they enter an opening called the pupil.
Student:
rays