Tonic Water!

"D'you want to go round by the lake on the way home?"

"No, the weather's dreary and I don't feel too bright!

"Aww! Come on, you know you'll feel better if you get a blip, then you can relax later."

"Oh, OK then"
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"Ha! Ooh! This is fun!"

"What's amusing you?

"I'm putting my camera down on the pebbles and I can't see the viewfinder to know what I'm taking a photo of!"