"When the children had studied morse code until dots and dashes swamin their heads even with their eyes closed..." Is this a hyperbole or an idiom? I'm pretty sure that this is an idiom.

Your preferation is correct.

Explanation:

It is an idiom because a group of words established by usage as having a meaning not deducible from those of the individual words is called an idiom.

Hope this helps

Have a nice day

This an example of hyperbole.

Explanation:

Hyperbole is characterized by exaggerated statements or claims not meant to be taken literally,

ex.:  I've told you to clean your room a million times!

ex.:  I am so hungry I could eat a horse.

ex.:  I have a million things to do today.

...while an idiom is a group of words established by usage as having a meaning not deducible from those of the individual words

ex.:  It costs an arm and a leg.

ex.:  Would you cut me some slack?

ex.:  She rubbed me the wrong way.

Can you see the difference??

do you have options?

particulars about treasure island, from the beginning to the end, keeping nothing back but the bearings of the island, and that only because there is still treasure not yet lifted, i take up my pen in the year of grace and go back to the time when my father kept th

explanation: