216. Blindness in Bats. One naturalist, trying to mystify Colonel Crackham, told him that he had studied the question of blindness in bats.

- I found,- he said, - that the ingrained habit of bats to sleep during the day in dark corners and fly only at night has led to the spread of blindness among them, although some individuals saw well with both or one eye. Two of the bats I examined saw with the right eye, three with the left, four did not see with the left eye, and five did not see with the right eye.

Could you calculate the smallest number of bats the naturalist had to examine to obtain such results?
216. The smallest number of mice is 7, with three possible cases:
1) 2 see well, 1 is blind only in the right eye, and 4 are completely blind
2) 1 sees well, 1 is blind only in the left eye, 2 are blind only in the right eye, and 3 are completely blind;
3) 2 are blind only in the left eye, 3 only in the right eye, and 2 are completely blind.