Answer based on context:

In week 4, the Lions traveled south to Arlington, Texas to take on the Dallas Cowboys. The Cowboys dominated the first half, putting the Lions in a big hole for the second straight week. First came a 25-yard touchdown catch by Dez Bryant. In the second quarter, Bryant scored again on a 6-yard touchdown catch. Dallas added more points with a 41-yard field goal by Dan Bailey. The Lions then got their only points of the first half with a 33-yard field goal by Jason Hanson. The Cowboys responded with a 35-yard field goal just before halftime. After the break, Dallas added more points with a 1-yard touchdown pass to Jason Witten, putting them up 27-3. The Lions responded with two consecutive defensive touchdowns: first a 34-yard interception return by Bobby Carpenter, then a 56-yard pick-6 by Chris Houston. The Cowboys scored their final points of the game with a 23-yard field goal late in the third quarter. In the fourth quarter, the Lions continued their comeback with a 23-yard touchdown catch by Calvin Johnson. They made it a three-point game with a 51-yard field goal by Jason Hanson, then Romo threw an interception to Stephen Tulloch, and took their first lead of the game late in the final quarter when Calvin Johnson caught his second touchdown of the game from 2 yards out to become only the second player in NFL history to record at least two touchdown catches in 4 straight games (the other to do so is former Vikings receiver Cris Carter). The Lions defense held off Dallas for the win. Like the previous week, the Lions came back and won it in the final moments of the game after being down by a large margin at halftime. This was also the largest comeback the Dallas Cowboys have ever allowed, and it is the largest comeback by a road team in NFL history as the Cowboys were up by 24 in the 3rd quarter. It was the first time the Lions started 4-0 since 1980. This also was its franchise-record fifth straight road win. Ironically, their last game at Dallas saw the Lions lose their franchise-record 26th straight road game.

How many yards was the longest interception return?
56