At that occasion I remembered the recently renewed interest, on the Internet, in the question why human males have no penis bone (baculum) and associated that scientific question with the pupil's question.
Look at the bacula of rats voles and squirrels featured at the Loom for example. The mere shape of these bones makes copula during pregnancy seem highly risky for the fetuses. Unless some sperm/mate competition scenario was conjured up, I'd bet these critters never mate during pregnancy.
The bacula of other mammals are not as spiny, pointed or barbed. Here's one from a raccoon.
|Raccoon baculum by Mordicai (GFDL, Creative Commons)|