Sphinx's Riddle

First think of a person who lives in disguise,
Who deals in secrets and tells naught but lies.
Next, tell me what’s always the last thing to mend,
The middle of middle and end of end?
And finally give me the sound often heard
During the search for a hard-to-find word?
Now string them together, and answer me this,
Which creature would you be unwilling to kiss?’