To get to the bottom of something:
Literally: To reach the lowest physical point – The cat’s trying to get to the bottom of
the drawer.
Figuratively: To get to the base or root of a matter to understand why a situation or problem exists – When she saw the broken window the teacher questioned all the students, one by one, to get to the bottom of the matter.
Other meanings for ‘bottom’
Noun:
At the lowest point – The cat’s getting the clothes from the bottom of the drawer.
Buttocks, haunches, the part of our body that we sit on – The cat’s bottom’s hanging out of the drawer.
Adjective
To describe something that’s at the lowest point – The bottom drawer.
So, in the video, The cat’s bottom’s hanging out of the bottom drawer as he’s trying to get to the bottom of it.