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A story of sorrow and comfort today, as Doctors Adam Rutherford and Hannah Fry investigate two mysteries sent in by listeners.

The Psychic Tear
Edith Calman challenges our scientific sleuths to answer the following question:
鈥淲hat is it about extreme pain, emotional shock or the sight of a three-year-old stumbling their way through an off-key rendition of Away in a Manger that makes the brain send messages to the lacrimal glands to chuck out water?"

Hannah discovers how the eye produces tears, with the help of Dr Nick Knight. Broadcaster Claudia Hammond, author of Emotional Rollercoaster, describes why Darwin experimented on his children until they cried. And, Adam watches a tearjerker to take part in a psychological study, but ends up getting angry instead.

The Tea Leaf Mystery
The team examine how to make the perfect cup of British tea, in response to Fred Rickaby from North Carolina:
"When we are preparing a cup of tea and the cup contains nothing but hot, brewed tea we need to add milk and sugar. My wife always adds the sugar first, stirs the cup to make sure it is dissolved and then add the milk. So, is that an optimum strategy for adding milk and sugar to a cup of tea?"

Adam consults Prof Andrea Sella from University College London about the chemistry of tea. Hannah visits a tea factory in Kent where Master Blender Alex Probyn teaches her an unusual method for tasting tea.

They conclude with the most important question: should you add the milk first or last? And, can tea professionals really tell the difference?

If you have any everyday mysteries for the team to investigate using the power of science, please email curiouscases@bbc.co.uk

Producer: Michelle Martin

Image: A woman holds a cup of tea, Credit: Thinkstock