"what is called" vs ", what is called, "

English as a Second Language English Vocabulary, Grammar and Idioms
1

Hi,
1 My mother is what is called a walking dictionary.
2 My mother is, what is called, a walking dictionary.

Are these both acceptable?
If so, which is more natural? Which do you prefer?
If so, what is the difference?

Thanks in advance!

2

.
Only #1 is acceptable.
.