a fly-on-the-wall film or television programme is one where the people involved forget or do not know that they are being filmed.

The five-part fly-on-the-wall documentary series focusses on the lives of three student nurses. (always before noun)

• If someone thinks, they've got another think coming!
• If the cap fits .
• If the cap fits wear it.
• if the going gets rough
• if the going gets tough
• if the worst comes to the worst
• If thinks something, they've got another thing coming!
• If thinks something, they've got another think coming!
• If thinks, they've got another thing coming!
• If thinks, they've got another think coming!
• if worst comes to worst
• If you believe that, you'll believe anything!
• if you can help it
• If you can't beat 'em!
• If you can't beat 'em, join 'em!
• If you can't stand the heat, get out of the kitchen.
• if you catch my drift
• if you get my drift
• If you pay peanuts, you get monkeys.
• if you play cards right
• if you play your cards right
• If you've got it, flaunt it!
• Ignorance is bliss.
• I guess so
• I have to hand it to