Dog returned. Stretched out inside. Or to get into mischief? (4,2)

I believe the answer is:

play up

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'dog' is the definition.
Although both the answer and definition are verbs in their base form, I don't understand how one could define the other.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for play up that I've seen before include "Hurt" , "Give you gyp - be on the blink" , "Malfunction" , "Emphasise the importance" , "Cause trouble" .)

I've seen this clue in the Sydney Morning Herald.

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