The Smudge Tool

Smudge - blends the pixels where you paint simulating the action of dragging a finger through wet paint.

This is how you use the tool:

The Smudge Tool spreads and mixes content of image areas:

• In the Toolbox, select the Smudge Tool.
• Choose brush size and style.
• Set the tool's strength.
• Drag on the image.
• In the Options bar, you can also specify the effect's "Mode"

 Sources:

Definition
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