Show of surprise that’s precarious (4-2-5)
I believe the answer is:
hand-to-mouth
This might be a double definition.
'show of surprise' is the first definition.
'hand to mouth' can be an answer for 'show' (I have seen 'Show of embarrassment' mean 'hand to mouth' so perhaps 'show' could also mean 'hand to mouth'). I'm not sure about the 'of surprise' bit.
'precarious' is the second definition.
(I've seen this in another clue)
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for hand-to-mouth that I've seen before include "Just adequate (subsistence)" , "Precarious (existence)" , "With barely enough to exist" , "Providing only bare essentials" .)