Horace Slughorn's hourglass was a clock made of two glass vessels connected with a narrow passage, with a green fluid flowing through inside. It had serpent imagery in its design, symbolising Slytherin house.
Slughorn already owned this object by the time that teenage Tom Riddle was studying at Hogwarts. The sand runs accordingly with the quality of the conversation: if stimulating, the sand runs slowly.
Appearances
- Harry Potter and the Half-Blood Prince (film) (First appearance)