@nn3x Confusion of those even happens to experts when conditions are noisy or marginal. To me they sound different because the rhythm is different.

Part of copying Morse, especially under difficult conditions, is your brain doing contextual analysis in real time. That comes to you after practice on the air. With numbers, you are often expecting to hear a number because of context, like WB_XYZ. Or if I send my SKCC number, you know that a string of numbers is coming.

The same with words. It's more likely the other person sent heard HERE and not SERE. This becomes easier with practice and when your speed comes up. You begin to hear whole words. At speeds above about 24 WPM you have to learn to copy whole words. All the "noise words" of English like the, then, here, there, can, etc. come into your brain effortlessly as whole words. The longer you've done it, the bigger your vocabulary becomes.

It gets better with practice. I'm still not happy when contesting and someone sends a difficult foreign call sign full of machine gun dits at 35 WPM or faster. Something like S57E can leave me scratching my head. Wait. What? My brain's context analysis doesn't help here.