Replace Function with Backslash in Snowflake

Escape Sequences:

Within a single-quoted string constant, a single quote character, along with other special characters, can alternatively be included in escape sequences. A backslash character (\) begins a backslash escape sequence.

Note that a non-special character escaped with a backslash is simply interpreted as that character (e.g. '\z' becomes 'z').

The string:

SELECT 'its a\b\c\d', '\\', '\\\\'
=>
its a<BS>cd, '\', '\\'

SELECT '\a', '\c', '\d'
=>
a, c, d

The symbol \b is the backspace character.

SELECT ASCII('\b');
=> 8

The REPLACE is trying to replace \(which does not existing in the input string) with \\ and it is a reason why it returns: its a<BS>cd

To perform the replacement the dollar-quoting could be used:

SELECT $$its a\b\c\d$$, $$\$$, $$\\$$;
=>
its a\\b\\c\\d