Would you describe a pit as "alive?"

[Viridian]

It's about perception. If you want to get the drama across, you portray the quicksand as something that threatens to pull you in. A person feels fear and curiosity when they don't know what the true nature of it is, and that's when we tend to personify natural phenomena, just as one can describe a storm or a fire actually trying to trap you in its deadly grasp. You could say that it makes your heart jump out of your body when it happens. Or it could be that your brain is sending impulsive signals to your vital organs to function at a higher level of intensity, providing more oxygen to your muscles to aid your body's systems in their survival. But that's no fun, is it?

Being serious though, it depends on how you want to feel. A calm person will think more rationally; whereas someone else will be driven by feeling and emotion. One can always cross over into the other realm of thought and experience quicksand in a whole other way.

[Duncan Edwards]

Hence the name "quicksand". It dates from a time when "quick" was often used to describe the difference between living and dead.

[bart1997]

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[water_bug_62208]

I like the view of quicksand or deep mud as being an inanimate substance that exhibits living attributes.

I enjoy the works of writers and animators who depict quicksand or mud as just a natural phenomenon, yet are able to instill lifelike qualities into the goo.

For example, in literature, using words such as "grip" and "grasp" to depict the naturally formed vacuum of the mire around the gal's feet and legs, or using the word "stretch" to symbolize the muck reaching out and holding on tight to its victim. And, in a sentence describing how a lady has lifted up on a mired limb, is not able to maintain the effort, and the mud pulls her back in is a cool way to animate the vacuum as a living response of the mud.

In animation, drawing the quicksand or mud stretching up and clinging tightly around the calves of a damsel does nicely to symbolize muddy hands grabbing the young lady in a relentless grip before jerking her back in.

And, when the gal simply stands still and doesn't fight, the quicksand or mud simply lies there lifeless as its particles of sand, clay, and/or silt yield to her weight as she sinks deeper.