P purchased a mini-trampoline from D. There were no instructions, but it did have sticker on it, stating: 'This product was designed to be used only as an exercise device. It is not designed to be used for acrobatics, trampolining, or any springboard type activities.' P used the trampoline for jogging. P eventually increased her time up to sixty minutes per day. P experienced severe pain in her ankles while walking. A doctor diagnosed her as having stress fractures in her ankles. P sued D for failure to warn. P testified the pain forced her to discontinue her work as a sales representative for a furniture manufacturer. P produced expert testimony which established relatively simple tests would have revealed the dangers. P's expert witnesses testified that long-term use of the trampoline could cause stress fractures in the affected ankle bones. D admitted it conducted no tests relating to the long-term effects of jogging on the mini-trampoline and did not systematically review published studies of mini-trampolines by sports medicine and exercise specialists. P's complaint about stress fractures was the first D had received. P got the verdict for $472,712 reduced by P's percentage of fault of thirty-eight percent. D moved for judgment as a matter of law in that P had failed to prove that D had knowledge of the danger. The district court held that D had no duty to warn about dangers it might have discovered by conducting reasonable tests. P appealed.