Here's what might be meant:
* "Bat your eyelashes": This idiom refers to a flirtatious gesture of rapidly blinking or fluttering one's eyelashes. It's meant to draw attention and convey interest in someone.
* "Blink rapidly": This is a more literal interpretation, and could be used to describe a variety of situations, such as surprise, shock, or even discomfort.
In any case, the number "forty" is likely meant to emphasize the frequency or intensity of the action.
It's always helpful to consider the context in which you heard this phrase to understand the intended meaning.