stump, mix up – cause to be perplexed or confounded; “This problem stumped her”
befuddle, confound, confuse, discombobulate, fox, bedevil, fuddle, throw – be confusing or perplexing to; cause to be unable to think clearly; “These questions confuse even the experts”; “This question completely threw me”; “This question befuddled even the teacher”
riddle – set a difficult problem or riddle; “riddle me a riddle”
elude, escape – be incomprehensible to; escape understanding by; “What you are seeing in him eludes me”