Section - The curious mark
Instead of touching the curious mark: say "You run your fingers along the groves of [the curious mark]. Buried deep inside the two small holes there seem to some kind of [buttons], but you fingers are just too large to reach them." Understand "grove/groves/circle" as the curious mark.
The small holes are scenery in the crypt. The description is "The holes are deeper than they look. Squinting to see in the bad light, you can make out some kind of button mechanism at the bottom of each hole."
The buttons are scenery in the crypt. Understand "button" as the buttons. Instead of examining the buttons: try examining the small holes.
Instead of pushing the buttons: try touching the curious mark.
Instead of inserting the rusty pair of nails into the small holes when the player is carrying the rusty pair of nails:
if the grave is in the crypt:
say "Nothing happens.";
say "There is a loud 'Click!' from the floor. Suddenly one of the large stone slabs swing open, revealing [a grave].";
now the grave is in the crypt.