It looks like he wants an infinite timer to evaluate after 10 seconds with a random message. (He probably doesn't want it to go for infinity, but that's what he put in the original code)
Code:
on !*:join:#: {
  timerCat 0 10 catmessage $chan
}

alias catmessage { 
  var %rand = $rand(1,7)
  if (%rand == 1) { msg $1 Meow }
  elseif (%rand == 2) { msg $1 Purr! }
  elseif (%rand == 3) { msg $1 *Licks myself clean* }
  elseif (%rand == 4) { msg $1 *Scratches my paws on the scratching post* }
  elseif (%rand == 5) { msg $1 *Yawns* }
  elseif (%rand == 6) { msg $1 *Curls up into a ball and falls asleep* }
  elseif (%rand == 7) { msg $1 *Rolls over onto my belly* }
}