Take the bull by the horns and the slug between the teeth (4,3,6)
I believe the answer is:
bite the bullet
'the teeth' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'take the bull by the horns and the slug' is the wordplay.
'take the bull by the horns' becomes 'bite' (I can't explain this - if you can you should believe this answer much more).
'and' means one lot of letters go next to another.
'slug' becomes 'bullet' (synonyms).
'bite'+'the'+'bullet'='BITE THE BULLET'
'between' is the link.
Can you help me to learn more?
(Other definitions for bite the bullet that I've seen before include "Deal with difficulty" , "Face up to trouble stoically" , "Face the music" , "Grasp the nettle" , "Be stoical" .)