There are many creatures that are so ininute that their existence is not perceptible. The falling of the eyelids even kills them.
सूक्ष्मयोनीनि भूतानि तर्कगम्यानि कानिचित्। पक्ष्मणोऽपि निपातेन येषां स्यात् स्कन्धपर्ययः॥