A 110-year-old lemon which was used for writing secret messages with its juice, and formed evidence to convict and lead to the execution of Karl Muller for spying for Germany in World War One is displayed, which forms part of ‘MI5: Official Secrets’, a new exhibition exploring the history of the British intelligence agency, at The National Archives in London, Britain, April 1, 2025. REUTERS/Toby Melville