Bloodspots caused by Billie-Jo Jenkins breathing out would look "very similar" to those caused by "impact spatter" created as she was being hit by her killer, forensic expert Duncan McKirdy told a jury at Lewes Crown Court.
Sion Jenkins, 40, denies murdering 13-year-old Billie-Jo at their home in Hastings, East Sussex on 15 February last year.
The prosecution alleges that 158 spots found on Mr Jenkins's jacket and trousers were created in a "blood mist" of impact spatter as he repeatedly struck Billie-Jo about the head with an 18-inch metal tent spike.
Mr McKirdy agreed with Camden Pratt QC, prosecuting, that the blood spots could have been caused by impact spatter.
"I have considered whether they could have got there as a result of her exhaling droplets of blood from the nose or whether this is a combination of both blood splattering and exhaling. I cannot say".
Mr McKirdy agreed that it was "unlikely" that the blood spots could have been caused by a bubble of blood bursting from within Billie-Jo's nostril.