I was happily tapping away at my keyboard in Gmail when upon hitting the send button I saw this error message
It says "You wrote 'are attached' in your message, but there are no files attached. Send anyway?"
Even though I wasn't actually referring to any attached files and had no plans to attach any, I was so happy to see that. I've both sent and received plenty of emails with no attachment only to have a follow-up 10 minutes later with a message saying "Oops. I forgot the attachment, here it is."
There's not much of an incentive for Google to spend time working on adding a feature like that and this is the only time I've ever seen it occur so it's not like they need to keep up with anybody in that regard.
A great thing is the sum of tiny details.