"Sweetbreads" isn't a scientific term. It's a euphemism some clever chef long ago gave the thymus gland and pancreas of veal, pork and lamb. Veal sweetbreads (which you're most likely to encounter in a restaurant) look something like white-meat chicken, when seared. Their flavor is very mild and ever so liveresque, and the texture is soft, almost creamy; it's the sort of food that takes well to other flavors yet keeps its distinct identity. Sweetbreads have always been popular among gourmands, and in past years one or two St. Louis restaurants might have featured them as a special. But over the past twelve months sweetbreads have been on the menu at Franco, Atlas, Balaban's and Bistro Alexander — and those are just the places we know about. It suggests we've reached a sort of tipping point between diners' growing knowledge and curiosity about food and chefs' desire to explore the culinary possibilities of the animal "from nose to tail," as the famed British chef and offal fan Fergus Henderson likes to say. We won't believe St. Louis has taken a step toward becoming a serious food town till we can order tripe at high-end restaurants as well as at our favorite taquerias and Vietnamese joints — but if the past twelve months are any indication, we're close.