Sibling non-rivalry.

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Originally uploaded by wailer2000.

These two are really getting along.

Allie will look at him and laugh.

Or, she'll say, "Loo-key, Loo-key, Loo-key!"

Luke will look at Allie and smile.

Or, he'll flex his eyebrows and study whatever she's doing.

Best of all, when she makes an impression him, he breaks out into a huge smile, belts out a squeak, and his whole body shakes.

She has the same effect on her dad too.