Her cocker spaniel named Willow appeared “bone dry” when spotted close to where Nicola went missing.
And while many people have speculated that this means Nicola did not fall into the river because her dog was dry, dog behaviour expert Ross McCarthy says it is not as simple as that.
He said: “It all depends on the dog’s association with water, and their relationship with the owner and so on, as to whether they would jump in.
“Some would through play or investigation and others would just mooch about on the side and some would panic at the strange situation."
An extensive search is ongoing to try and find Nicola Bulley (Image: PA)
Mr McCarthy added: “Dogs go into fight or flight as we do, but they may not perceive the same dangers as us.
“Often chemical changes in the body of the owner can alert the dog to an unusual situation but naturally if the owner is not present - that won't be the case.
“Presumably this dog has been walked along the canal and water often and been discouraged from going in or naturally just avoided going in.”
Nicola Bulley's heavy clothing may have weighed her down in river
He added: “It would be a strange occurrence from the dog’s perspective - but outside of Disney and in exceptional cases - dogs don't jump in to save owners.
“It's no different to when you jump in a swimming pool - the majority of dogs - unless conditioned otherwise will just circle the pool.”