You get your foot stuck in and then the tide comes in and you drown.

Most quicksand I'm aware of is in tidal flats [0] [1] and it really is dangerous to take a short cut over them. Come to think of it, most normal sand I encounter is in tidal flats, too.

[0] https://www.98fm.com/news/north-dublin-beaches-quicksand-war...

[1] https://www.independent.co.uk/travel/southend-on-sea-deadly-...