Is this grammatically correct?
There is nothing like an animal attack video to remind one of their mortality.
Use one's to be consistent.
There is nothing like an animal attack video to remind one of one's mortality.
Carl Mason Franklin, To Carolyn with love, 1998, p.284:
In telling the Trustees of my affection for WSU, I made the point that one should never forget one's roots.
I long for the days when it was socially acceptable to use 'his' in this context. Not because I think of the world as masculine, but because we really need a pronoun that works without argument in these situations.
The original phrasing 'to remind one of their mortality' has been gaining ground, and may one day be accepted usage, but the word 'their' really is a plural pronoun and confuses the clarity of the statement. Kris's solution of "one's" works, but moves further into the realm of sterile constructions and impersonal language.
Here's a three-part answer:
Don't use 'their'. It is a plural pronoun, and although everyone understands it in this context, it creates an unpleasant tension between the singular 'one' and the plural 'their'.
If possible, rewrite the sentence to eliminate the gendered pronoun, either eliminating the need for a pronoun, or using a plural construction. For example,
Animal attack videos are a great reminder of mortality.
There is nothing like an animal attack video to remind us of our mortality.
Use a gendered pronoun when it is contextually appropriate:
Susan said, "There is nothing like an animal attack video to remind one of her mortality."