How big does Linda think are shower drains?

I am watching House Of 1000 Bounces (S6E12) and Bob is afraid of a pigeon that found its way into the restaurant.

When they reveal that "his" root of that fear comes from an old Alfred Hitchcock movie she says there is other stuff to be afraid of. For example to slip through the shower drain.

How big does she think is a shower drain? 😂