Curly vs. Do/End

Ruby discovery for today: curly braces have a different precedence than do/end. That is, these two expressions mean different things:
user.houses.map { |h| h.verified = false if h.hide_avm?; h }.to_xml
user.houses.map do |h| h.verified = false if h.hide_avm?; h end.to_xml
I’m still unsure what the second one means, but I do know that it doesn’t work.