A dictionary of Confusable Phrases: More Than 10,000 Idioms and Collocations

give it a second thought • have second thoughts
give it a second thought—reassess an opinion or decision pre-
viously made: You may think this will happen in the distant
future but if you give it a second thought you’ll realize it is
already happening.
Note:
The expression is not antonymous in meaning to the
phrase don’t give it a second thought—(also: don’t give it a
thought) 
1
. dismiss it from your mind; let that not worry you:
Don’t give it a second thought, until you are a lot older and
have more experience. 2. is used to indicate that thanks are
unnecessary: Oh, don’t give it a second thought, Hun! Actually
I should be thanking you! 3. is used as a polite way of accepting
apolog y: I looked at her and said graciously: “Please don’t give
it a second thought. I wasn’t offended.”
have second thoughts—(also: get second thoughts) realize that
one may be mistaken; have doubts: I am starting to have sec-
ond thoughts about my purchase based on what I am reading
here.
Note:
The expression is not equivalent in meaning to the phrase
have another think coming
— used of a need to reconsider one’s
plans or opinions: Those who think Carter is still respectable
company should have another think coming.
See also: think again / think twice.
give it a shot • give it the gun
give it a shot—(coll.) give smth. a try; attempt to do smth.
unfamiliar: I don’t know if my recording skills are up to par
but I just might give it a shot.
give it the gun —(coll.) cause a vehicle to accelerate rapidly:
Even when I would stand in the road and make motions to
help me, they would turn out around me and give it the gun.
give it mouth • give mouth
give it mouth —(dated) speak with vigor and intensity: “Tell
us your name!” said the man. “Pip, sir.” “Once more,” said
the man, staring at me. “Give it mouth!”
give mouth —(also: give tongue) 
1
. utter one’s thoughts;
express smth. in words: I have an opinion of you, sir, to which
it is not easy to give mouth. 2. (of a dog ) bark when on the
scent: There are hounds that do not give mouth. Some have
been trained that way, some come natural.