The last trading session has been a mixed one for U.S. stocks. Among the top ETFs, (SPY Quick QuoteSPY - Free Report)  gained about 0.1% while (DIA Quick QuoteDIA - Free Report)  and (QQQ Quick QuoteQQQ - Free Report)  moved 0.1% and 0.2% lower on the day.

Two other specialized ETFs are also worth watching as both saw higher-than-normal trading volume. In fact, both the funds experienced volume levels that were more than double their average for most part of the last trading session. This could make these ETFs the ones to watch out for in the days ahead to see if the trend continues.

BNDX: Volume 3.49 times average

This international total bond market ETF was closely watched yesterday as about 7.88 million shares changed hands. This compares to the average trading volume of around 2.23 million shares and BNDX lost about 0.07% in the session.

The big move was probably the result of a slight uptick in yields amid the possibility of aversion in another U.S. shutdown and U.S.-China trade talks. The fund has added about 1.2% in the past month.

BIB: Volume 3.22 times average

This double-leveraged biotech ETF was in the spotlight yesterday as nearly 633,000 shares moved hands compared with an average of roughly 196,800 shares a day. The fund gained about 1.2% in the last trading session.

The movement can largely be credited to the BioRestorative Therapies’ developing of a therapy ''ThermoStem.'' The news along with other sector-specific tailwinds like strong merger and acquisitions and increased demand for drugs in the developing markets led to the uptick in volume. For the month, IBB is down about 0.6%.

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