It's pronounced 'mouzle' by the locals. I learnt this from Rick Stein, I think. I learnt from another source that it's so-named because the harbour is tiny and the entrance to it from the sea between the two piers is tiny. Eventually, the pronunciation changed from 'mouse hole' to 'mouzle'.
I had a vegan Cornish pasty here; it was nice; much better than the one I had yesterday in Sennen Cove.
Like the rest of Cornwall that I've seen, Mousehole is very steep.
Oh, and we saw a cat.