How do you tell someone?

Mom has gotten into a habit of taking big gulps of juice, and holding it in her mouth. Now, that in and of itself, isn't serious or bad even. What is serious, is that 9 out of 10 times she chokes on it, because honestly, she has forgotten it is in her mouth.

Either that, or she is trying to dissolve the pills she takes, which is also a no no, according to the pharmacist.

Yet when I tell her, that she needs to swallow, not hold the fluid in her mouth, she gives me this blank stare, as if wondering what I am talking about. On some occasions, she has even said she doesn't do it, which is hard to dispute, given she says it, while having the liquid in her mouth.

So how do you tell her?

A nurse suggested using a firm authoritive voice, and commanding she swallow, which to me, sounds wrong. Not only that, I simply can't do that, because she is Mom, and I am her son.  You don't strip a person of their dignity, but you do need to find a way to get the needed result, which in this case, is to swallow while drinking.

And I haven't a clue how to do this, yet.