How can I get an imprint of the lock?

Hint 1 of 6:

You'll need something that can mold itself into the shape of the lock.

Hint 2 of 6:

Something that's often very squishy.  Look around at each of the named
guards to see what they all have.

Hint 3 of 6:

Otalopicus is chewing on some gum.  But you'll have to convince him to open
his mouth long enough for you to get it.

Hint 4 of 6:

Try annoying all of the guards to see if Otalopicus will react to any of
them.

Hint 5 of 6:

Bug Rustic (W) and Otalopicus will leave his mouth open.

Hint 6 of 6:

Then you can reach in O's mouth to take his gum (F).