It's more fractal if you consider the B. to be a regular expression:
b='Benoit B. Mandelbrot';for i in {0..2};do echo "$i : $b";b=$(echo "$b"|sed 's/B./Benoit & Mandelbrot/g;');done
0 : Benoit B. Mandelbrot
1 : Benoit Be Mandelbrotnoit Benoit B. Mandelbrot Mandelbrot
2 : Benoit Be Mandelbrotnoit Benoit Be Mandelbrot Mandelbrotnoit Benoit Be Mandelbrotnoit Benoit B. Mandelbrot Mandelbrot Mandelbrot
b='Benoit B. Mandelbrot';for i in {0..2};do echo "$i : $b";b=$(echo "$b"|sed 's/B./Benoit & Mandelbrot/g;');done
0 : Benoit B. Mandelbrot
1 : Benoit Be Mandelbrotnoit Benoit B. Mandelbrot Mandelbrot
2 : Benoit Be Mandelbrotnoit Benoit Be Mandelbrot Mandelbrotnoit Benoit Be Mandelbrotnoit Benoit B. Mandelbrot Mandelbrot Mandelbrot