In the mainland Chinese drama series I'm watching now on YouTube, there's a scene (今生有你 epi.2) with the construction workers taking a lunch break.
To leave their hands free to open the lunchbox, they park the chopsticks inside (not across) the mouth, so that they stick out of the mouth. Watching this, my immediate reaction was, "NO NO NO!".
As children, we were taught never to do that with cutlery. A sudden jolt (e.g., the person's head tilting forwards from being accidentally bumped into from behind) will result in an injury to the throat.
Another instinctive reaction from my upbringing is to instantly look for, and pick up, food morsels that have fallen out of one's mouth, whether it's onto one's own clothing, the table or the floor.
The original source behind this practice is cooked rice grains (common ingredient in a Chinese household) that have dropped onto the floor, as they're squidgy, so they must be tracked down immediately and removed before they get trodden on, squidged into the bottom of one's foot/feet (in the tropics, we go barefoot in the house) or footwear.
This, in itself, is a horrible enough feeling which then entails more work, washing out the sticky mess, but worse, it gets spread around the house, leaving squidgy patches on the floor for other people to step on.
(Singapore, 1960s)