Which letters are difficult to pronounce if one has a lisp?

A lisp primarily affects the pronunciation of "s" and "z" sounds. Here's why:

* Lisp: A lisp is a speech impediment where the tongue is placed against the front teeth instead of the alveolar ridge (the bony ridge behind the teeth) when producing these sounds.

* "s" and "z" sounds: These sounds are produced by forcing air through a narrow channel formed by the tongue and the alveolar ridge. When the tongue is positioned incorrectly, the air escapes through the front teeth, resulting in a "th" sound instead of "s" or "z."

Therefore, words containing "s" and "z" sounds are typically difficult for someone with a lisp to pronounce clearly.

Example:

* "sun" becomes "thun"

* "zoo" becomes "thoo"

* "sister" becomes "thithter"

However, it's important to note that the severity of a lisp can vary, and some individuals may also have difficulty with other sounds, such as "sh" and "ch."