What is a word for "about to burst out laughing"?

Is there a word that can describe this facial expression?

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("about to burst out laughing")


Solution 1:

The picture shows a laugh that is smothered.

Solution 2:

Not a particularly common word even with its primary meaning of impregnated with thorium oxide to increase thermionic emission, but...

thoriated - tittering; being or sounding of nervous or suppressed laughter