An IMO flaw in Nethack is that if you travel with the '_' command and
an umber hulk confuses you, the game continues with the travel command
execution instead of aborting it. That way it may be disastrous if you
travel on Medusa's level and a newly created random umber hulk appears,
leading you straight into the water without possibility to just stop.
If, OTOH, you do a command repetition '.', waiting for, say, blindness
or confusion to wear off, this will be interrupted.
https://groups.google.com/d/msg/rec.games.roguelike.nethack/WNAjM1ip0EQ/GAwVdTnc8D4J