Sherlock Season 4: 20 Easter Eggs & References From The Six Thatchers

9. Toby The Bloodhound

When on the hunt for the killer, Sherlock recruits Craig's bloodhound Toby to sniff out the scent.

The mutt with the mighty nose appears in exactly the same capacity here as he does in Doyle's The Sign of Four. Disney fans, meanwhile, will recognise him from his animated appearance in Basil the Great Mouse Detective.

On a side note, the scene where Sherlock, John and Mary comedically wait for Toby to get going was improvised on the day of filming, as they struggled to get the dog playing Toby to move.