tl;dr: he was walking with it and tripped, and his ass landed on it and it slipped in.

if a “terrifying line is being crossed” every day, how does that affect you? Is each line a new horror? or do they all blur together?

About 33 seconds into the clip there is a squelching fart noise. It aligns with the lady in green’s quickly-stifled horrified reaction. The fart noise had a wet component to the sound, as if liquid was oozing out in addition to gas. It’s quite probable that he ended the meeting because he gave himself a mud ring and had to go wipe it and change his diaper.