*Il ne faut pas courir deux lièvres à la fois = You must not have too many irons in the fire.
Il a une mémoire de lièvre = He has a memory like a sieve.
[Also: Il est comme les lièvres, il perd la mémoire en courant.]
Il veut prendre les lièvres au son du tambour = He makes a great noise about what should be kept secret; He divulged a plan which to succeed had to be kept secret.
Ligne
C’est un homme hors ligne = He is a first-rate man. (See [Hors].)
Il est en première ligne = He is in the front rank.
Linotte
Il a une tête de linotte = He is a hare-brained fellow.
Livre