W, while "==" is comparison, "||" is boolean, so "rat" || "mouse" evaluates "rat", thus fails your document.write statement.
"rat" && "mouse" --> "mouse" (And)
"rat" != "mouse" --> true (not equal)
W, while "==" is comparison, "||" is boolean, so "rat" || "mouse" evaluates "rat", thus fails your document.write statement.
"rat" && "mouse" --> "mouse" (And)
"rat" != "mouse" --> true (not equal)