Sister Teresa is walking down to breakfast when she meets another nun walking up.
"Good morning, Sister Assumpta!" says Sister Teresa. "Good morning, Sister Teresa!" says the other. "Did you get out of bed the wrong side this morning?"
Puzzled, Sister Teresa continues on her way to the refectory. "Good morning, Sister Pieta!" she says to the nun serving porridge. "Good morning, Sister Teresa!" says the other. "Did you get out of bed the wrong side this morning?"
Now the tiniest bit miffed, Sister Teresa goes and eats her porridge, then as she is returning her bowl and spoon for washing she notices the Mother Superior. "Good morning, Reverend Mother!" she says, trying not to wince in anticipation. Sure enough, the Mother Superior asks the same as the other two, and Sister Teresa is on the verge of tears. "Why is everyone asking me that? Have I been rude? Do I look bad-tempered?" she wails.
"Oh no, dear!" says the Mother Superior. "It's just that you're wearing the Bishop's slippers."