x = np.array([1,2,3])
y = np.array([4,5,6])
df = pd.DataFrame({"numpy": [x,y]})

df["numpy"].mean() #works as expected
Out[231]: array([ 2.5,  3.5,  4.5])

df["numpy"].std() #does not work as expected
Out[231]: TypeError: setting an array element with a sequence.

df["numpy"].values.mean() #works as expected
Out[231]: array([ 2.5,  3.5,  4.5])

df["numpy"].values.std() #works as expected
Out[233]: array([ 1.5,  1.5,  1.5])

df["numpy"].dtype
Out[235]: dtype('O')

df["numpy"][0].dtype
Out[236]: dtype('int32')

df["numpy"].describe()
Out[237]:
count             2
unique            2
top       [1, 2, 3]
freq              1
Name: numpy, dtype: object

df["numpy"]
Out[238]:
0    [1, 2, 3]
1    [4, 5, 6]
Name: numpy, dtype: object