Never use an adverb to modify the verb 'said' . . . he admonished gravely. To use an adverb this way (or almost any way) is a mortal sin. The writer is now exposing himself in earnest, using a word that distracts and can interrupt the rhythm of the exchange.
Elmore LeonardI used to be able to write five pages a day, every day, no problem. Now a good day is five or four pages, and that's from 9:30 A.M. until 6 P.M.
Elmore Leonard