When you change your mind
Get cold feet
When you accept/understand an idea
Getting your head around it
When you say no to something
Put your foot down
When you look very serious
Keep a straight face
When you pay attention on something
Keep an eye
When you have direct experience of something
Come face to face
When you say the wrong thing
Put your foot in it
When something attracts your attention
catch your eye
When you get on with someone
See eye to eye
When you feel unable to do something
can't face