Final answer:
The main idea of the sentence is that eating ice cream too fast can cause a short-lived headache known as a "brain freeze," which typically lasts around 30 seconds.
Step-by-step explanation:
The main idea of the sentence "Sometimes when you eat ice cream really fast you get a headache. This "ice cream headache" usually lasts about 30 seconds." is that consuming ice cream too quickly can cause a brief, sudden headache, often referred to as an "ice cream headache" or "brain freeze."
This phenomenon is a common experience and is typically short-lived, usually resolving within half a minute. This type of headache is a result of the rapid cooling and rewarming of the blood vessels in the palate or the back of the throat.
The main idea of the sentence is that eating ice cream really fast can sometimes cause a headache, also known as an "ice cream headache." This headache typically lasts about 30 seconds. It is not fully understood why this happens, but it may be due to the sudden cold temperature affecting the blood vessels in the head.