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