Dog neutered yesterday and today he has had a lot of erections?

I had my pup (6.5 months old) neutered yesterday....this evening he's had several erections - which appear to be more than just a "little red rocket". He did have one testicle that hadn't descended, so he has 3 incisions in total as they had to search for the other one.

I'm not sure if this is related to the procedure or not, just find it a bit strange. I will be phoning my vet in the morning to see what she has to say about it, in the mean time I don't think it's a problem, but just don't know. Apparently this is common in horses...but obviously my pup isn't a horse :)

Thoughts?