What you don't know

You go for a swim
In a nice fresh lake
What you don't know
Is your brain I will take

I come ever closer
As you play in the sun
What you don't know
Is I'm about to have fun

Up through your nose
Through the olfactory nerve
What you don't know
Is the mission I serve

I will eat your brain
It's my cafeteria
What your don't know
I am Naegleria

For those unaware, Naegleria fowleri is an amoeba that livesucks in fresh water lakes that goes up the nose and basically eats the brain.