full of beans 的用法在美国十分流行。

吃了一肚子豆子，天知道会怎么样！

一种说法是：科学家们认为，豆类含丰富维生素，对人的健康十分有益。

人们经常吃豆类当然可以"精力旺盛，神采飞扬"喽！

你看，The children were full of beans when they were told the picnic would be held the next Friday.

当孩子们得知下周五要野餐时个个兴高采烈。

所以，full of beans 为精神饱满，兴高采烈的意思。