1someone is silent
the cat got someone’s mouth
2something or someone that looks extremely untidy, or something that is very badly done
a dog’s breakfast
3someone who keeps something that they do not want in order to prevent someone else from getting it
a dog in the manger about
5to waste effort on a futile task, a lost cause, or a topic that's already settled
flogging a dead horse
6someone has escaped, run away, or is no longer available, indicating a missed opportunity or a person's departure
the bird has flown
7a person, a country or a situation that seems or claims to be powerful or dangerous but is not really
a paper tiger
8create a whole new set of problems
open a can of worms
9you have many good opportunities in front of you
the world is your oyster
10very competitive
(a case of) dog eat dog
11the act of matching people with suitable jobs or tasks
horses for courses
12in a bad mood; in an angry way
like a bear with a sore head
13leave it alone, leave something in peace
let sleeping dogs lie
14something that you particularly dislike
pet peeve / hate
15the best choice, or your favorite option
pick of the litter