If there be one transient feature more than another which should be avoided in a painting, and particularly in the principal figure, it is a wide-open mouth. Necessarily, after a short acquaintance with a picture containing such a feature, either the mouth appears to be kept open by a wedge, or, as in the case of a laugh, the face is likely to wear an abnormal expression approaching to idiocy, for it is altogether contrary to experience of normal persons in real life, for a mouth to be kept open longer than for an instant or two. Hence the first artists have studiously refrained from exhibiting a wide-open mouth, or indeed one that is open at all except to such an extent that the parted lips appear a permanent condition. But a few great men have erred in the matter. Thus, Mantegna shows the child Christ with the mouth widely open in a half-vacant and half-startled expression, which is immediately repelling.[a] Dosso Dossi has several pictures much injured by the feature,[b] and in Ercole di Roberti's Concert, no less than three mouths are wide open.[c] One of the figures in Velasquez's Three Musicians opens his mouth far too widely,[d] while Hals has half a dozen pictures with the defect.[e] A rare mistake was made by Carlo Dolci when showing Christ with His mouth open wide in the act of utterance,[f] and Mengs erred similarly in St. John Baptist Preaching.[g] In more modern times the fault is seldom noticeable among artists of repute, though occasionally a bad example occurs, as in Winslow Homer's All's Well.[h] Even when an open mouth seems unavoidable, the effect is by no means neutralized.[i] [a] Virgin and Child at Bergamo. [b] Notably A Muse Instructing a Court Poet, and Nymph and Satyr, Pitti Palace. [c] National Gallery, London. [d] Berlin Gallery. [e] See Merry Company at Table, Met. Mus., N. Y., and similar pictures. [f] Christ Blessing, a single figure picture. [g] Hermitage, Petrograd. [h] Boston Museum, U. S. A. See Plate 15. [i] As in Dow's The Dentist, Schwerin Mus., and a similar work at the Louvre.