to slap one's thighs to be surprised 1 realization
NEW Realization 1
Type Polysemy
Language Meadow Mari
Lexeme эрдым пераш
Meaning 1 to slap one's thighs
Direction
Meaning 2 to be surprised

 Меке кува эрдым савалтен колта, шинчам каралтен йырымла…


The old woman Mekhe slapped herself on the thighs, stared and started squealing

Reference Mari-Russian idiomatic dictionary
Comment

The direction of the shift is evident from the non-compositionality of the second meaning. To use this lexeme in the second meaning the state of surprise probably must be accompanied with the action of slapping one's thighs