The Impossible (2012)
Frequently Asked Questions
It didn't come from the opposite direction. After they got hit by the first wave, the water changes direction and flows back into the ocean, meaning that the second wave was also coming from the ocean. This is unclear in the film, yes, but with a little common sense, this can be deduced. Think about how waves break normally on a beach: the wave comes in and washes on the shore and is pulled back out, what's called "undertow". The same principle applied in this scene only on a much larger scale.
Most likely it's a piece of seaweed. Though we don't see what happens, a piece of seaweed had somehow forced its way down her throat while she was struggling underwater. The force of the water rushing inland had probably filled Maria's throat faster than she could realize and a lot of water was forced into her stomach with the seaweed.