What does "thumbs" mean?

English Language Tests, Intermediate level

ESL/EFL Test #723 [color=blue]“Real Life: Using Body Parts as Verbs (3)”, question 5

My father loves to read the newspaper every morning. Every day, as he sips his morning coffee, he slowly through each page of the paper.

(a) knees
(b) thumbs
(c) arms
(d) faces

English Language Tests, Intermediate level

ESL/EFL Test #723 [color=blue]“Real Life: Using Body Parts as Verbs (3)”, answer 5

My father loves to read the newspaper every morning. Every day, as he sips his morning coffee, he slowly thumbs through each page of the paper.

Correct answer: (b) thumbs

Your answer was: [color=green]correct
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What does “thumbs” means here?

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Browse, read.
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thanks Mister Micawber, your explanation is very concise and clear.Regards