Why are you so weak

A man called his mother in Florida: "Mom, how are you?"

"Not too good!" said the mother, "I've been very weak."

The son said: "Why are you so weak?"

She said: "Because I haven't eaten for 38 days."

The man said: "That's terrible. Why haven't you eaten for 38 days?"

The mother answers: "Because I didn't want my mouth to be filled with food if you should call."