From Cecil B. DeMille's Autobiography
(Prenctice Hall, Inc., 1959)
In one scene, Crichton (Thomas Meighan) saves Mary (Gloria Swanson)
from a leopard by killing it with his bow and arrow. He then drapes
the dead animal over his shoulders as he talks to Mary. DeMille
said the traditional method for staging such as scene would be
to use a stuffed animal, but no matter how good the taxidermist
or the cameraman may be, the animal will not look real. So, DeMille
heard of a leopard at the Selig Zoo they were planning to destroy
because it killed a man. DeMille asked for and was given the live
animal on the promise that it would be executed prior to being
used in the picture.
When DeMille saw the animal, he felt it was too beautiful
to be killed and chose, instead, to chloroform
the animal for the scene, much to the dismay of Meighan and the
entire crew. They did, indeed, chloroform the animal, and when
it came time to make the scene, the animal was sleeping soundly.
Meighan hoisted the leopard around his neck and began reciting
his "lovemaking" lines to Swanson. However, in the middle
of his monlogue, the leopard began to dream. "In that sleep
of chloroform, what dreams may come to a man-killing leopard,
I cannot say, but the leopard also began to talk in his sleep,"
DeMille said. "First, cozy sighs and purrings, then low,
contented growls, then, as the drama of his dream progressed,
more ominous snarls and snorts issued from the head that was nuzzling
close to Tommy Meighan's ear."
Meighan's line was supposed to be "I know I have paid through lives and lives, but I loved you then and I love you now." With the leopard carrying on so, Meighan, instead, said, "I know I have paid through lives and lives - Mr. DeMille, the damn thing is waking up! - but I loved you then and - get me out of this, I tell you he's coming to!"
DeMille said he continued to assure both Meighan and Swanson that everything was OK, and they made it successfully through the scene. Actually, it took the animal another whole day to come to completely. He turned out to be a gentle creature, and DeMille said they named him . . . Crichton, of course.
From Gloria Swanson's autobiograhy Swanson on Swanson (Random House, 1980)
The last scene Gloria Swanson filmed for "Male and Female" was the Babylonian sequence in which she must descend some steps into a pit of lions. Not only was this dangerous, it was made more so by the heavy costume she wore which literally required additional help to carry when she was not on the set.
There are two parts to the sequence with the lions - when she descends the steps into the lions' den and the shot of her lying on the floor with a lion across her back.
In the first part, she must open a wooden gate to enter
the lion's den which she said was made of flimsy, painted wood
and would break easily if a lion decided to jump against it. As
she nervously approached the gate, the trainers turned the lions
loose. Although they were not supposed to come near her at this
point, one came to the gate and bounded out of the den a few feet
from her. She stood motionless, frozen with fear, and one of the
trainers scooped her up off her feet and carried her to safety
while another trainer 
returned
the lion to its den.
After a break, they began to film the scene again. Once more, a lion came toward the gate. "I was afraid to turn my back on him. Men behind me were calling instructions, but I stood absolutely still. The lion and I stared at each other, hypnotized, until a trainer stepped in front of me and drove him back with a whip and a chair."
At that point, DeMille said he had all the footage he needed and suggested they delete the scene with the lion across Swanson's back. Swanson protested saying she wanted to do the scene because it was a recreation of one of her favorite paintings, "The Lion's Bride."
Swanson lay on the floor in the lion's den. "They put a piece of canvas on my back to keep the lion's manicured claws from making the slightest scratch," she said. "Then they brought the lion up to me and put his paw on the canvas. Ever so slowly they pulled the canvas aside until I could feel his paw on my skin. Every hair on my head was standing on end. I could hear the camera grinding and then the crack of the trainer's whip. Every cell in my body quivered when the animal roared. His hot breath seemed to go up and down my spine."
When the scene was finished, Swanson looked up among the specatators and saw her father there with a look of horror on his face at the proceedings and at having found his only daughter in such a dangerous situation. Fortunately, the shot was a success and proved to be pleasing not only to DeMille but Swanson, as well, and, possibly, the most recognized still shot from the movie.