like how steep the hills are, is it muddy, is it stoney? and even if there's angry landowners nearby. ramblers maps shows the status of paths in different colours and volunteers use it to check what needs surveying. purple shows new paths yet to be audited, like the one we're standing on, and then the green shoes are completed path. just looking at the map, you can see the majority of the 40,000 miles of paths still need to be audited. but if more volunteers come out and enjoy notjust the walks but the technology too, the team will only get closer to achieving their aim. now, earlier in the programme, we'd met back up with gav, from the slow mo guys, to film a rocket engine test at 80 times slow motion. that's 2,000 frames per second. and here's how we got on. we're in a nice, flat part of texas.