It's amazing what people discover Google's algorithm suggesting. In the case of autocomplete the search box tries to work out what you might be searching for in advance and gives you a few suggestions.
Imagine your surprise if two out of the four suggestions for
[my cat is]suggests you may be the father of kittens.
It's most likely that the search is due to people looking for this Yahoo! Answers question in which someone actually asks whether they could have got their cat pregnant. Yahoo! Answers is the home to so many dumb questions it can be hard to sort the really odd questions from planted fake questions.